How do you guys that use these organize your data, test name, load name etc? Have you got any tips or tricks you've learned with the unit you could post here? Also any problems? I have a photo album with some pics and some comments you guys might find helpfull. How do you find your filing method to work for you? I figured a topic like this could be a interesting to those that use them.

Oehler 43 PBL album

I spoke to those guys last week and I was told the whole package ready to go was $970.00 so you are including the cost of a cheepo laptop?

I too hate all the associated gear lugging around at a range. It would be very convenient to have a cable or wireless to get the signal back to the comp which would be on the front seat of the truck!

As for calibration why couldn't you fire five cartridges, beginning with a low load, then increase 2 grains, this builds a calibration curve from which you can begin working?

Hotcore and Roger,

First - I'm not trying to convince anyone it's absolute psi data in the thread here, you well know it's "relative" only to the factory ammo selection we have availible (for most of us anyway). With that, I have a much easier time accepting this data around the maximum pressure area than that of the psi ring type you use, both are relative, but only the Oehler 43 provides a better reference ie. barrel stretching the same amount, IMHO. Brass which is considerably thicker at the "base" has potential to be a good indicator, but in my opinion not comparable from one case to another or calibrated by any means.

Second - The tests I've made using factory ammo are quite impressive as to their consistancy and relativity to SAAMI specs. Even you would be amazed at the results, given the facts you describe, which one would think leads to large errors, readings are just too close ALL the time to be off by much at all.

Dentons method for getting inside measurements vs. measuring the case body itself adds how much more accuracy? I don't know, but just using the case has worked fine for me. I have not had one factory round produce more than 64k psi TOPS in any chamber I've tested thus far. It's a strange thing how most book loads don't lie much either on their max loads.

Another note, I've tested several loads to just over 70k psi and almost 80% never had unusual bolt lift at that point, most reloaders would use this as another indicator if not a primary one. I have not tested up farther to see when 80-90% get a noticable difference in lift, but it would be up there for sure, farther than I'd want to subject my rifle to every time I worked up loads.

70k psi is usually about 1-2gr over the 65k psi point but can vary how fast it rises, just depends. I can give you a list of 60k, 65k and 70k psi loads for you to make the observations and comparisons if you like?

Could you post a picture of where you measure the cases for psi and give suggestions on how it's done to get maximum accuracy? I will at some point have a chance to compare the results to the Oehlers indications and make a list of the findings.

Roger,

I make up my own calibration ammo, it is loaded up to identical psi as the factory ammo produces and is used to check before tests are taken. This is much cheaper than buying the factory stuff and produces nearly as consistant psi ES with good prepped brass. Factory stuff is highly underrated stuff these days, it can be very very consistant and hard to equal, but the savings and ability to taylor a load to the rifle will always be worth it. Often velocity is even hard to match at the same psi.

Take care,

Hot Core,
I too haven't any experience on the Oehler M43 PBL, but I have had a fair amount of time measure pressures via strain gauges. Since most of your commentary applies to Strain measurements in general I'll try to give my input there.

1 & 2) You are right, calibration is one of the challenges presented by measuring pressures by Strain - if you need to put an exact psi number on your measurement. If all you need to do is measure pressures of a load relative to another benchmark load, Strain does this exceedingly well.

If you have to put a psi number on your Strain readings, calibration can be accomplished theoretically using thick walled pressure vessel (barrel) and thin walled pressure vessel (brass casing) equations. I pursued this route and had my gunsmith give me the reamer dimension at the point I desired. He marked that corresponding point with dychem on the outside of the barrel and I obtained my necessary measurements. As Brent has noted, the taper of the chamber, while theoretically a concern, proved to be a non-issue in practice.

There are experimental means to calibrate the gauge (that are more involved). You could use pressurized oil or hydraulic fluid and use an accurate calibrated high pressure dial gauge. But thankfully I haven't found that to be necessary.

Like Brent, I've shot different types of factory ammo to check if the Calculated pressures corresponded to supposed SAAMI spec pressures. Thankfully they did quite nicely, and I keep a large quantity of this "reference ammo" to check my system before I start a session.

3) The Strain Gauge attachment to the barrel can be unsightly - yes. In a typical bedded bolt action, it can potentially be mounted on the underside (with proper relief of the stock provided a bedding pad is not present). My primary application is measuring pressures on an AR TestBed. A special barrel nut allows access to the chamber, and aesthetics are not a concern.

4)Yes, Strain Measurements off a barrel are surrogate measures (as is miking a case head, as is copper crusher, as is recoil accelerometers). In fact the only direct pressure measurement is via piezo transducers.

Taking measurements off the pressure ring is still a surrogate measure of expansion of the a pressure vessel and present problems of it's own. The most significant I feel is that it does not always show expansion until safe pressures are well exceeded. Brass is not uniform in hardness, thickness and springback from brand to brand, from piece to piece, even the same piece from firing to firing. And Pressure Ring Measurement is subject to the same calibration problems that you cite for Strain Measurements. Do you KNOW that .0001 expansion (or whatever measurement you're using) correlates to 50,000 psi or other pressure? Plus it has the added disadvantage of being binary - it's either "yes, it's max" or "no, it's not". There is no telling of degrees. What would you say the sensitivity of Pressure Rings are? 1000psi, 2000psi? I can tell you that I feel comfortable saying that Strain's are sufficiently sensitive to pick up a 1000 psi difference when correlating that difference with a change in velocity.

Lastly, Miking is subject to measurement error. I'm sure you can appreciate the difficulties in measuring a cylindrical body precise to 1/10,000 of an inch. At .0001" expansion due to heat from your hand, oil on the case or a speck of dust can impact your measurement.

Here's a discussion on another board on Pressure ring measurements. There are two very significant participants on that thread. SE Watson (OK Shooter) and Ken Howell (protoge of Homer Powley). It's a long thread, well worth the read if you watch for those posters contributions.
http://talk.shooters.com/room_48/8525
5) Yes the Oehler PBL System can be expensive. But it's when you add the acoustic target that you run into the range you're talking about. Folks with good electronic backgrounds can potentially rig their own Strain Measurement device. The Gauges themselves are the heart of the system and they run $10 to $20 each. The circuitry is basically a bridge to read the change in voltage caused by the change in R across the gauge. Add an output device of your choice (cheap digital oscilloscopes work fine) and you're in business.

6) My whole strain setup fits into a shoebox with half the space left over. Setup consists of plugging in the lead, turning on the unit and zeroing out the range. 1 minute tops.

[ 02-07-2003, 20:45: Message edited by: Chris F ]

Chris,

I can't disagree with you on anything there, you said it better than I as well. You appear to know way more than I do about the strain stuff.

Have you found any interesting paralells with bolt lift at given pressures?

What unit do you use for strain measurement?

Outstanding post, Chris! Very well put.

Suggesting that measuring deformed cases of unknown composition is more accurate than actual strain measurements is ludicrous.

747's would not be flying today without "speculative data" from strain guages.

Yo Chris, when I asked what would be the least outlay of cash to be up and running the man who answered the phone said, "$970.00". I then said, "I just want to measure the pressure, I will buy the chronograph stuff later", "well you need the box and the software and gauges so that would be $970.00". It seems to me the box with its internal circuitry to change the analog signal to digital is what they want $800.00 for.

I have some software here called Labview (data capture) and a buddy of mine gave me a catalog and pointed out exactly what I needed to get going. I simply haven't had the time to begin putting it together yet.

Hey Brent & Chris, I'm just getting in from the field and off to bed.

Yes I have a picture and yes I have a complete File on using Pressure Ring Expansion which I can email. You only need to have "Word and Excel" on your computer.

Good discussion which I'll be glad to respond to in the morning.

Hotcore,

I have Word but don't have Excel. Can you post em here?

Sleep tight.

Roger,

If you want, email me sometime if your going out to Birchwood shooting and I might meet up with you. I usually go out next to my place here but go that way with my dad occasionally, we use the solid benches at the 300 yard range to measure from while using the acoustic target. I figure I'll head there to shoot some 178 A-Max loads I found some promise in with my Ultra when the wind dies back down before it gets cold again.

Take care,

Hey Brent, Do you happen to have Speer Manual #11, #12 or #13? If you do, I can point you to a picture in one of them.

This is quite long, but I'd recommend reading it through twice. A lot of the detailed explainations for "tricks" and how to do the actual measurements are close to the end. Some measurements are not taken in a "Normal Manner" and those are the "tricks" to getting accurate data.

I'll work off-line on your other questions and repost.

...

Here are the "condensed versions" of Case Head Expansion(CHE and Pressure Ring Expansion(PRE):

..........CHE/PRE General Summary..........

1. Fire a Factory round.
2. Measure the “widest diameter” across the Pressure Ring with 0.0001” capable Micrometers.
3. Record this value as the Pressure Ring Expansion(PRE) on a Data Sheet
4. Calculate the PRE Average for the entire box of cartridges.
5. Record the PRE Average on the Data Sheet and on the box the cartridges came in.
6. This establishes the “Factory Standard Pressure Value” for this specific Lot of cases. This PRE Average will be used as the MAX Pressure Ring Expansion acceptable during Load Development.
7. Make a note that the cases have been “Fired 1 time” on the Data Sheet and the box.
8. Reload this Lot of cases with your first “Test Loads”.
9. Before firing, measure across the Case Head in one specific spot and record this value on “a new” Data Sheet.
10. After firing, re-measure the Case Head in the exact same spot and record.
11. Subtract the “before firing” dimension from the “after firing” dimension and record as the Case Head Expansion(CHE).
12. After firing, measure the PRE and record.
13. Repeat both CHE & PRE measurements for all Test Loads.
a. When Case Head Expansion reaches 0.0007” on your reloads, STOP.
b. When Pressure Ring Expansion reaches the same value as the “Factory Standard Pressure Value”, STOP.
14. If neither value in #13 is reached, note “Fired 2 times” on the Data Sheet and the box, and reload the cases with an incremental increase in the Powder. You must use the same Lot of Primers, the same Lot of Powder, the same Lot of Bullets and the same Bullet Seating Depth.
15. Continue the Testing until a 0.0007” Case Head Expansion is attained or the “Factory Standard Pressure Value” is duplicated.
16. You have now created a SAFE MAX Load for this Lot of cases.
17. This Load can be SAFELY duplicated in Lots from the same manufacturer where the weight of those cases is the same or less.
18. This SAFE MAX Load is for this one specific firearm ONLY!
19. Changing to a “New Lot” of any component used in the Load requires that you re-verify the CHE & PRE.

..........Details and Explanations..........

Case Head Expansion(CHE) can be “tricky” to read for a beginner. So can properly setting up a Sizing Die, determining the proper bullet Seating Depth or getting an Oehler M43 Strain Gauge properly attached to the chamber. With practice, and knowing how many shots have been through your cases, you can determine when to STOP increasing the Powder in your Load resulting in a SAFE MAX Load. This method will tell you for sure when you have reached an Un-SAFE Pressure. Yet, in my opinion, CHE is NOT AS RELIABLE an indicator as Pressure Ring Expansion(PRE). PRE is fairly straight forward and easier to quickly get a grasp on.

When taking the CHE & PRE measurements, you will use the Micrometer slightly different in order to obtain the most accurate values. When measuring CHE, you will use the ratchet feature on top of the Micrometer spindle to determine when the anvils are at the correct tension against the case head. When measuring PRE, you will set the Micrometers “just tight enough on the case to keep it from falling out from between the anvils”.

You measure CHE in one specific spot on the Case Head. CHE measurements must be taken before and after firing. I like to align the Micrometer with one of the numbers or letters found stamped into the case head. Turn the “ratchet” until it slips and read the Micrometer. Record that value for the “before firing” Case Head measurement on the Data Sheet. Lets say you measured 0.4121”. (Note: The numbers used throughout this paper are all fictional.) Fire the round and remeasure the case head in the same exact spot. Lets say you measured 0.4125”. Record the “after firing” measurement on the Data Sheet. The difference between the two measurements is the CHE. Subtract 0.4121” from 0.4125” and your CHE is 0.0004”.

When measuring PRE, you will be rotating the Pressure Ring on the case inside the Micrometer Anvils to locate the “widest diameter”. You must be careful not to deform the Pressure Ring by “forcing” it to turn between the anvils. Once you locate a tight spot, open the micrometers slightly and turn the case until you locate the “widest diameter”. For an example, lets say you get a measurement of 0.4772” at the widest diameter. Loosen the Micrometer to 0.4773” and see if the widest diameter on the Pressure Ring will “hang” between the anvils. If it won’t hang, record 0.4772” as your PRE measurement. You only measure PRE after the round has been fired and record that value. Loosening and tightening of the Micrometers does take a small bit of time to make sure you are recording a repeatable value. But, it goes real fast once you get used to it. You will get to the point that you can do it with one hand holding the case and the other hand adjusting the micrometer.

1. On Belted cases (7mmMag, 375H&H, etc.), CHE is measured across the Belt.
2. On Non-Belted cases (223Rem, 7mm-08, 30-06, etc.), CHE is measured just forward of the extraction groove (where the Belt would normally be located) with special “Thin Blade” Micrometers.
3. On Straight Wall cases (9mm, 357Mag, 444Mar, 45-70, etc.), CHE is measure just forward of the Rim with special “Thin Blade” Micrometers.
4. On a “fired” Belted case, PRE is measured across the “widest diameter” of the case body forward of the Belt.
5. On a “fired” Non-Belted case, PRE is measured across the widest diameter on the case body forward of the Extractor Groove.
6. On a “fired” Straight Wall case, PRE is measured across the widest diameter on the case body forward of the Rim.

The Pressure Ring is located in the same spot on the case body where Head Separations occur. If you have a Speer #12 Manual, look on page 72 and it is where the cases have split in the bottom two pictures.

In order to measure PRE, you will need to either P-FLR or FLR Bottle Neck style cases and FLR Straight Wall style cases between shots. Neck Sizing will not reform the case wall properly for these measurements. Once you know where the SAFE MAX Load level is located, then you can go to Neck Sizing if you so desire.

Adjusting a FLR Die to P-FLR is done by “slightly raising” the FLR Die higher in the press than normal. When adjusted to P-FLR properly, the bolt closes on an empty, length-trimmed case, with a slight bit of resistance. This indicates you have a crush fit between the case-head/case-shoulder and the bolt-face/chamber-shoulder. That ensures the longest possible case life, helps prevent case-head separations and increases the accuracy potential of your rifle/load combination. This is also referred to as “Zero Headspace”.

CHE measurements vary considerably on the very first firing of a new case. This is why you do not bother to measure them on the initial firing of the Factory rounds. If you desire to see the variance, just measure the factory rounds on the initial first firing. I do not recommend this for novice reloaders since it will create confusion for you as to why that is so. CHE measurements become more reliable for firings 2-5. Then CHE measurements become somewhat unreliable after 5-7 firings, depending on the strength of the previous Test Loads. This is due to “work-hardening” of the brass in the case head.

If you are using a Non-Belted or Straight Wall case, you will need to buy a set of “Thin Blade” Micrometers to measure CHE and the Thin Blade Micrometers can be expensive, $160 or so. But, I found a nice used set in a Pawn Shop that was asking $50. I got them for $25. On a Belted case you can measure CHE with regular $35-$45 Standard Anvil Micrometers.

PRE is measured using regular Micrometers whether the case is Belted, Non-Belted or Straight Wall. PRE measurements can be taken on the same cases 7-10 times, depending on the strength of the previous Test Loads. PRE is useable on ALL firearm cases and is the best method of the two. I encourage the use of both CHE & PRE so you end up with an additional set of Pressure Indicators, but a person can get by with PRE alone.

The Micrometers must be 0.0001” capable in order to be accurate enough for all of these measurements. A 0.001” capable Caliper is just not accurate enough and will mislead you if you try to use them, making all your Expansion Measurement data worthless and dangerous.

Chris -

quote:

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Here's a discussion on another board on Pressure ring measurements. There are two very significant participants on that thread. SE Watson (OK Shooter) and Ken Howell (protoge of Homer Powley). It's a long thread, well worth the read if you watch for those posters contributions. http://talk.shooters.com/room_48/8525.cfm

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Phew!! You're right, it certainly IS a long read (not quite as long as our MatchKing thread, tho.. ), and, if I understand Dr. Howell correctly, we are really putting our lives on the line by using "traditional" pressure measuring methods, or, even by using loading manual data. Is that your take on it?

R-WEST

Hey Brent and Chris, I’m selecting portions of your all’s posts to respond to. If I miss something important, let me know. These are simply my thoughts on these issues.

Brent – I'm not trying to convince anyone it's absolute psi data in the thread here,

HC: That is good to hear you understand that much about it. You are already ahead of most folks that have them. The problem as I see is when an inexperienced Reloader looks at a Load that gives a psi reading and thinks, “It worked for him, so it should work for me too.”

Brent - I have a much easier time accepting this data around the maximum pressure area than that of the psi ring type you use, both are relative, but only the Oehler 43 provides a better reference ie. barrel stretching the same amount, IMHO. Brass which is considerably thicker at the "base" has potential to be a good indicator, but in my opinion not comparable from one case to another or calibrated by any means.

HC: I understand your logic, but respectfully disagree. I do agree that both “are relative measurements”. The “case” will always be the best place to determine if a Load is SAFE because it is “the weakest link” in the firing process. As you know, your barrel will handle Pressures well beyond what the actual case can withstand. If we were “testing the barrel”, then the Strain Gauge information would be more relevant, because it is taking expansion data directly from the barrel.

But, when Developing Loads, we should be more concerned about not exceeding the Elastic Limit of the actual Cases. And the only way to know what the SAFE MAX is for a specific Case Lot, is to see when the Pressure Signs(CHE/PRE) indicate the elastic limit has been reached. (Or STOP when Book MAX is reached irregardless of what CHE/PRE indicates.) Then we need to back-off from that amount of Powder. Reading the M43 psi data just doesn’t tell you when the elastic limit is reached.

The only way I know to Calibrate the M43, to what I’d consider an acceptable confidence level, is to use special Loads provided by SAAMI. And, I’m pretty sure SAAMI doesn’t make them accessible to people outside a Ballistics Lab

Brent - Dentons method for getting inside measurements vs. measuring the case body itself adds how much more accuracy? I don't know, …

HC: I’ve no idea either.

Brent - 70k psi is usually about 1-2gr over the 65k psi point but can vary how fast it rises, just depends.

HC: I agree completely with, “it can vary with how fast it rises”. The rate the Pressure increase varies due to the Burning Rate of the Powder and the Drag of a specific Bullet as it transitions the bore. Since each Lot of Powder/Bullets is slightly different, and since the dimensional variations between firearms also influences the “pressure rise”, I don’t believe the folks that post their M43 psi values with a Load, really understand it “ONLY” applies to their specific firearm and has the potential to mislead a beginning reloader.

Brent - I can give you a list of 60k, 65k and 70k psi loads for you to make the observations and comparisons if you like?

HC: I really appreciate the offer, but I just don’t have the time this Spring and Summer to do it justice. Maybe Chris would be interested.

Brent - Could you post a picture of where you measure the cases for psi and give suggestions on how it's done to get maximum accuracy?

HC: No, I can’t post a picture in this Thread, but I can email you a picture of where the PRE is located. Or, I can reference you to a picture in one of the Speer Manuals. Or, in my last post(near the end) I tried my best to describe where the Pressure Ring is located on the different case types.

Hey Brent, If I missed giving my thoughts on something above, let me know.

...

Chris - I too haven't any experience on the Oehler M43 PBL, but I have had a fair amount of time measure pressures via strain gauges.

Hey Chris, Me too! I’ve got over 30 years as a Design Evaluation Engineer/Manager.

Chris - If you have to put a psi number on your Strain readings, calibration can be accomplished theoretically using thick walled pressure vessel (barrel) and thin walled pressure vessel (brass casing) equations. I pursued this route and had my gunsmith give me the reamer dimension at the point I desired. He marked that corresponding point with dychem on the outside of the barrel and I obtained my necessary measurements.

HC: Well Chris, that is without a doubt the best method I’ve seen outside of actually doing the measurements with a CAD/CAM machine. Of course, the reamer info isn’t available for factory rifle chambers.

Chris - As Brent has noted, the taper of the chamber, while theoretically a concern, proved to be a non-issue in practice.

HC: I’m having trouble with the, “non-issue in practice”, thought process. Any variation in the dimensions of the wall, or a slight skewing of the Strain Gauge placement(from the measurement point) results in changing the data that the M43 provides. Again, it gets back to realizing the data from the M43 can be skewed up or down depending on quite a few inter-related things.

If a person had the resources, it sure would be interesting for someone to attach 3 Strain Gauges side-by-side, around a barrel and hook them to 3 separate Pressure Indicators. If the Strain Gauge theory is accurate, they would all read the same. However, my experience with Strain gauges leads me to believe they would never coincide in value, nor would the “delta value” coincide.

Chris - There are experimental means to calibrate the gauge (that are more involved). You could use pressurized oil or hydraulic fluid and use an accurate calibrated high pressure dial gauge. But thankfully I haven't found that to be necessary.

HC: I was under the impression (mistaken perhaps) that the M43 Strain Gauges were “non-removable” once installed. Are you saying a M43 Strain Gauge “could” be attached to a Certified Pressure Vessel, tested, removed and then reused on a barrel?

Chris - Like Brent, I've shot different types of factory ammo to check if the Calculated pressures corresponded to supposed SAAMI spec pressures. Thankfully they did quite nicely...

HC: I sincerely mean, “best of luck to both of you using the Strain Gauge method”.

Chris - The Strain Gauge attachment to the barrel can be unsightly - yes. In a typical bedded bolt action, it can potentially be mounted on the underside (with proper relief of the stock provided a bedding pad is not present). My primary application is measuring pressures on an AR TestBed. A special barrel nut allows access to the chamber, and aesthetics are not a concern.

HC: Amen on unsightly. Sounds like you figured out a fairly acceptable way to tolerate them.

Chris - Yes, Strain Measurements off a barrel are surrogate measures (as is miking a case head, as is copper crusher, as is recoil accelerometers). In fact the only direct pressure measurement is via piezo transducers.

HC: Correct me if I’m wrong, but I believe all the piezoelectric devices, like the Clerke(SP?), require a special barrel and are a destructive (to the case) style test. Of course, the Copper Crusher is destructive. So, neither of those methods are useful outside a Lab.

Chris - Taking measurements off the pressure ring is still a surrogate measure of expansion of the a pressure vessel and present problems of it's own. The most significant I feel is that it does not always show expansion until safe pressures are well exceeded. Brass is not uniform in hardness, thickness and springback from brand to brand, from piece to piece, even the same piece from firing to firing.

HC: I believe this is covered in my last post on CHE/PRE. And of course you wrote this prior to that being posted. But, I disagree with, “it does not always show expansion until safe pressures are well exceeded.” Granted there are some “tricks” to using measuring CHE/PRE, but they are easy to understand and easy to perform. The only real concern in taking the measurements is it is slower than reading a value off an LCD screen. But, that allows my barrels to cool a bit more between shots, so I look at it as an acceptable use of my time.

Chris - Do you KNOW that .0001 expansion (or whatever measurement you're using) correlates to 50,000 psi or other pressure?

HC: No, but that doesn’t matter with PRE. One of the very best advantages of using CHE/PRE, is because you get to use the multi-million dollar Quality Labs of the Factories to establish the SAFE SAAMI value in this exact Lot of cases. The Factories determine when it is time to STOP adding Powder in the cases based on all their Test Equipment(most of which you listed above). Then all we need to do is see what the PRE is “in our specific firearm” using those cases to establish a Benchmark Standard for the Expansion of that specific Lot of cases.

Chris - Plus it has the added disadvantage of being binary - it's either "yes, it's max" or "no, it's not". There is no telling of degrees.

HC: Chris, I respectfully disagree. If the CHE/PRE measurements are taken as I described in my last post, you will be able to see the Expansion Values increase in a linear direction as the amount of Powder is increased in a Test Load. Try it yourself, exactly like I posted it, and you will see what I mean.

Chris - What would you say the sensitivity of Pressure Rings are? 1000psi, 2000psi?

HC: I’ve got no idea. But, it doesn’t matter since the Benchmark from the Factory ammo keeps this method from getting a person into Pressure Problems.

Chris - Lastly, Miking is subject to measurement error. I'm sure you can appreciate the difficulties in measuring a cylindrical body precise to 1/10,000 of an inch. At .0001" expansion due to heat from your hand, oil on the case or a speck of dust can impact your measurement.

HC: You are correct. You will not get the “Same Exact PRE Data” from case to case with the exact same Load, it will vary slightly. But, it will surprise you as to how consistent they can be.

Of course, the same is also true for the data taken from the Strain Gauges. By that I mean if you put the same exact Load in 3 cases and the first one measures 55,367psi on the M43, I’d bet neither of the other two loads will measure “exactly” 55,367psi.

Am I right?

So, holding the same “data accuracy requirement” to both systems seems only reasonable to me. People forget they calibrated with an “unknown”, measured a tapered surface, and may have skewed the attachment of the Strain Gauge. Due to that, I believe it is improper to think of any Strain Gauge reading as “exact, infallible, absolutely reliable” data either.

Chris- My whole strain setup fits into a shoebox with half the space left over. Setup consists of plugging in the lead, turning on the unit and zeroing out the range. 1 minute tops.

HC: Sounds like to me you need to give the M43 some competition. Put it on the market.

...

I’m not suggesting if you have a M43 or a set-up like Chris’ that it should be tossed in the trash. They provide one more piece of Pressure input for us to be aware of, even if it is “questionable”.

I am suggesting you can do it SAFER, cheaper and with a lot less concern about the data being “accurate” by just going with the relatively cheap 0.0001” capable Micrometers.

HC,

I've read your last post, havn't had a chance to look at your data and specific method in the other post yet, I will later. I appreciate your time in explaining it to me.

There are many things I disagree with and want to and will respond to reguarding last post, but I've got to work on other things right now so I'll get into that later. I type pretty slow and you'd laugh if you watched how long it takes me sometimes. I've got to get this chamber reamer thing worked out on a rifle my smith is waiting to get started.

Hot Core,
Before I reply in detail to your latest post, I thought I'd thank you for your explainations of your PRE Method and cut to my biggest question on your method. BTW, it appears to match very closely, Ken Waters method that he detailed in the first volume of Pet Loads.

Here's where I'm losing you. If I understand correctly, you are using a factory cartridge as a reference for Peak Chamber Pressure not to be exceeded.
You are then comparing expansion on your reloads to this reference standard (factory ammo).

1) Brent and I are doing similar with the Strain measurements. We are taking factory loads and using them as a reference standard. Where we differ is that we can use many different factory loads to see how they correlate to the expected Pmax. That appears to be a luxury you do not have since you are tied to a specific brand/lot of brass for your results to be valid. Why is our use of a factory standard invalid where your use is okay?

2) If you are taking measurements from the first firing of Factory ammo, how do you get around the cited unreliability of expansion on first firing?...

quote:

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CHE measurements vary considerably on the very first firing of a new case. This is why you do not bother to measure them on the initial firing of the Factory rounds.

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3) Calibrating with a factory standard has pitfalls. It assumes that factory ammo is safe and near maximum in your barrel. That has proven to be not always the case (see linked thread). There's been a prevalent problem with Federal 223 Match ammo showing severe pressures only in some guns, yet not in others (my strains showed less than SAAMI).
[/QUOTE]Now the line items;

quote:

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Well Chris, that is without a doubt the best method I�ve seen outside of actually doing the measurements with a CAD/CAM machine. Of course, the reamer info isn�t available for factory rifle chambers.

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My gunsmith John Holliger gets the credit for that. He knew what I was doing and made the suggestion. I would guess with the appropriate measuring tool (perhaps a sufficiently long tubing or ball mic) greater precision could be attained.

quote:

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I�m having trouble with the, �non-issue in practice�, thought process. Any variation in the dimensions of the wall, or a slight skewing of the Strain Gauge placement(from the measurement point) results in changing the data that the M43 provides. Again, it gets back to realizing the data from the M43 can be skewed up or down depending on quite a few inter-related things.

---

Your post was in regard to my experience that in spite of the varying barrel thickness under the gauge, the pressures correlated nicely with the expected SAAMI pressures of factory ammo. What can I say? It correlated. You're apparently able to make the leap for PRE and factory ammo. I will say that the attachment and positioning of the gauge is important. Good lamination in crucial and like you mention, any mounting angle introduces a cosine effect that would underestimate the strain measurements (if calibrated theoretically albeit in a consistent fashion). If relative pressures are all you're doing, then even a cosine effect is of no consequence.

quote:

---

If a person had the resources, it sure would be interesting for someone to attach 3 Strain Gauges side-by-side, around a barrel and hook them to 3 separate Pressure Indicators. If the Strain Gauge theory is accurate, they would all read the same. However, my experience with Strain gauges leads me to believe they would never coincide in value, nor would the �delta value� coincide.

---

It's more important that a given gauge give good accuracy (they do) than maintain the consistency from gauge to gauge (they still do as well though). However that is actually an interesting question, not necessarily for your reasons. Strain Gauges are tested and certified by the manufacturer. They come with a pedigree and I would expect them to perform within tolerance. Your question is interesting because of a conversation I had with a friend with a Oehler M43. He felt that measuring strains just ahead of the throat might give similar strain readings as would directly over the chamber. I had been considering mounting them serially along a barrel to test that. I do not know that mounting them in the fashion you suggest would be practical just because there's only so much room to fit them radially.

In response to my sharing an experimental calibration method;

quote:

---

I was under the impression (mistaken perhaps) that the M43 Strain Gauges were �non-removable� once installed. Are you saying a M43 Strain Gauge �could� be attached to a Certified Pressure Vessel, tested, removed and then reused on a barrel?

---

I failed to mention that the strain gauge remaines in situ and the barrel is the actual vessel to be pressurized. Definitely involved and potentially hazardous.

quote:

---

Chris - Like Brent, I've shot different types of factory ammo to check if the Calculated pressures corresponded to supposed SAAMI spec pressures. Thankfully they did quite nicely...

HC: I sincerely mean, �best of luck to both of you using the Strain Gauge method�.

---

Please explain how it differs from your calibration with factory ammo? (Assuming my understanding of your use of factory ammo is correct).

quote:

---

Correct me if I�m wrong, but I believe all the piezoelectric devices, like the Clerke(SP?), require a special barrel and are a destructive (to the case) style test. Of course, the Copper Crusher is destructive. So, neither of those methods are useful outside a Lab.

---

I agree and beyond that, the data provided by Piezo has probably less correlation to "real life" than either of our methods. Here's why;
1) The obvious is that it's not pressure read off of firing in your specific barrel.
2) Piezo is commonly used with a Universal Receiver, which for reasons beyond the scope of this discussion is very prone to user technique and provides very variable results.

quote:

---

HC: Chris, I respectfully disagree. If the CHE/PRE measurements are taken as I described in my last post, you will be able to see the Expansion Values increase in a linear direction as the amount of Powder is increased in a Test Load. Try it yourself, exactly like I posted it, and you will see what I mean.

---

I disagree with your disagreement! The relationship between PRE and charge delta may be linear, but the relationship between charge delta and pressure certainly is not. Therefore, PRE and pressure do not have a linear relationship. I will try to play with your method to satisfy my curiosity, but I would ask that you beg, borrow or steal a Strain setup to give yourself first hand experience as well.

quote:

---

Of course, the same is also true for the data taken from the Strain Gauges. By that I mean if you put the same exact Load in 3 cases and the first one measures 55,367psi on the M43, I�d bet neither of the other two loads will measure �exactly� 55,367psi.

---

To state that strain measurement should be exactly the same for each firing is a surprising statement coming from you. Velocities for a given load can vary considerably...yet we don't question the chronograph. Rather we work to minimize this variation in the load. An absence of absolute repetition of readings is not a failing of the device but rather in this case an indicator of the variability of the effect. It's worth noting that when Vaughn experimentally calibrated his strain gauges, he found that the repeatability was within "a few tenths of a percent". Applied to your 55Kpsi example is less than a 1000psi tolerance. Acceptible for me. Not even a dream for PRE.

quote:

---

So, holding the same �data accuracy requirement� to both systems seems only reasonable to me. People forget they calibrated with an �unknown�, measured a tapered surface, and may have skewed the attachment of the Strain Gauge. Due to that, I believe it is improper to think of any Strain Gauge reading as �exact, infallible, absolutely reliable� data either.

---

Absolutely! Same calibration criticisms apply to both. And correlating the calibration readings to the "tapered surface", your theoretical concerns appear to be unfounded (where did we use that before).
Nothing human is exact "infallible, absolutely reliable etc". but I will offer that used properly (a caveat that applies to both methods), strain measurement can offer greater sensitivity, accuracy and flexibility than can Pressure Ring Expansion Measurements.

Hot Core, please read the linked thread. It's illustrative of the shortcomings and potential dangers of the PRE type pressure extrapolations. BTW, aside from being Homer Powley's heir apparent, Ken Howell was also the long-time editor of Handloader Magazine. And for an additional carrot, his foil in that thread is a proponent of the PRE technique with some good points and technique refinements along your lines.

I see the PRE Method analogous to the Ballistic Pendulum and the Strain Devices more akin to Chronographs. Welcome to the 21st century!

[ 02-05-2003, 14:48: Message edited by: Chris F ]

Hey Brent, HA, I'm not that fast a typer either, so this is eating up a bunch of time. But, I do enjoy discussing this with folks who's opinion I respect.

Hey Jon A, I'm working on a response off-line.

Chris: "Hot Core, please read the linked thread. It's illustrative of the shortcomings and potential dangers of the PRE type pressure extrapolations. BTW, aside from being Homer Powley's heir apparent, Ken Howell was also the long-time editor of Handloader Magazine. And for an additional carrot, his foil in that thread is a proponent of the PRE technique with some good points and technique refinements along your lines."

Hey Chris, I didn't respond to this portion before because of two people you mentioned, stanley and howl. Let's just say I do not respect their opinions and I'll drop it at that.

Chris: "I see the PRE Method analogous to the Ballistic Pendulum and the Strain Devices more akin to Chronographs. Welcome to the 21st century!"

HC: Hanging on to the best, old time-proven methods available to reloaders is one of my greatest strengths!

Hot Core,
I'm most curious about your comments on Calibration and if my read on our two methods using factory cartridges is accurate.

Is there a difference between your use of factory cartridges any different than Brent's and mine? And how did you reconcile your feelings that a first firing did not yield accurate PRE measurements?

That I see key to your arguments against Strain. Everything else we'll have to agree to disagree.

Jon A: “I simply don't agree. Yes, the cases are the weakest link. If your loads are all on the ragged edge of failing the case then maybe that would be safer. But your loads shouldn't be that hot.”

Hey Jon A, I’ve no problem at all disagreeing with someone. But I agree that I don't load to the point that the cases fail.

I guess I should have mentioned in the beginning my primary reason for posting to any Thread is to either keep a beginner out of trouble or provide an alternative, experienced method to achieve some goal.

But it is a great pleasure to be able to sit back and rationally discuss our different methods with you, Brent and Chris.

...

Jon A: “Having primer pockets only stay tight five or six loadings instead of 10 isn't a safety issue to me. You are still way below failing it. Brass is cheap, throw it away and buy some more.

What I'm concerned about is the action. If that comes appart, it's going to hurt. I'm concerned about how much stress I'm putting on the action. That's what matters to me safety-wise. The worry is subjecting the action to repeated over-max loads will fatigue it and make it fail someday.”

HC: Jon, those two paragraphs seem to be in conflict to me. In the first one you say only getting 5-6 reloads per case is OK, but you are concerned about stress on the action.

I want SAFE MAX reloads in my rifles too, but I desire a bit longer case life than you.

Jon A: “One of these days I'll get around to doing a full fatigue analysis on the recoil lugs in my action to see just how big a worry this really is but until I do I want to stay on the safe side.”

HC: What method will you use to do that? I understand Magna-fluxing. Is that what you will use?

Jon A: “That's what a strain guage gives you that nothing you can measure on the case can--it will tell you how much your load is stressing the action relative to another load. It will do so accurately. Much more accurately than measuring cases.”

HC: I simply disagree. The CHE/PRE Methods have been in use since reloading first began. Their track record is indeed old, but that time span has shown they work extremely well and are totally SAFE.

They also allow a beginning reloader to learn about case Pressure without an excessive cost. I’ve discussed(and argued) the point about keeping time-proven methods available for the beginners. Some of them would never be able to reload if they had to wait to purchase the $2000 M43 + Laptop.

Jon A: “Say you get some really tough brass. You've strengthened the weakest link. Do you really want to crank up your loads 5 KSI just because the brass can handle it? I wouldn't. If you get some really soft brass that wears out quickly with your favorite load does that mean you're risking your life every time you pull the trigger? No, it just means you need to buy brass more often.

HC: One of the great benefits of CHE/PRE is to be able to detect the exact concerns you have, and then be able to make adjustments in the Load to compensate for them.

Jon A: “If the strain guage reads the same with both brands of brass, you know you're stressing the action the same amount and operating with the same margin of safety for your action with both loads. That's what I'm interested in. You can't get that measuring cases.”

HC: Excellent point.

Jon A: “I haven't decided whether I'll get the Oehler or one of the cheaper set-ups, but I will get one soon. My plan when I get it? Remarkably simple compared to what you describe above:

Work up a load using known components just like I always do, like MILLIONS of people have been doing for a century with a remarkably good safety record--keep adding powder until I see a visual pressure sign then back off a few grains. Then measure the pressure of that load. Done.”

HC: That is a good plan. And if you would add CHE/PRE as you Develop the Load, it would be excellent.

Jon A: “Regardless if the guage says 61,000 psi or 69,000 psi I don't care because it isn't calibrated absolutely. Whatever it says is The Limit. That's as hot as I feel comfortable loading my rifle. That's as much as I want to stress my action. That's the limit.

From then on, each new load will simply be a matter of working up to that pressure level. Never again will I have to exceed it in order to observe visual pressure signs so I can back off again. I can go right up to it and know I'm max before the brass does.”

HC: Jon, I agree with you all the way up to the last sentence, but there I disagree.

Jon A: “Different brass, bullets, powder, etc--it doesn't matter. The peak strain measured is directly proportional to the peak stress to which I'm subjecting my action. Same reading, same pressure regardless of how much this particular lot of brass decides to expand or not expand.”

HC: How much a specific Lot of cases expands is what interests me the most. Granted it is not nearly the concern today that it was years ago, but we used to get widely varying extremes in the “temper” of caseheads, even from the same manufacturer. Using CHE/PRE, it is easy to see a variation from Lot to Lot. But, ALL available Pressure Indicators should be used that the reloader has at his disposal, not just one method.

Jon A: "So explain to me how that can be safer if your loads are nowhere near the pressure levels required to actually fail the brass and you replace the brass frequently."

HC: With the conditions you outline, I agree it is not necessarily Safer. But it is certainly less expensive for a beginner to be able to verify his loads.

Best of luck to you Jon A.

Chris: “BTW, it appears to match very closely, Ken Waters method that he detailed in the first volume of Pet Loads.”

HC: I learned the CHE/PRE Methods from my Elders back in the late 1950’s / early 1960’s. And I agree it is very close to Ken Water’s and Bob Hagel’s methods. A person could simply go by what they outline and do just as well as the way I go about it.

Chris: “Here's where I'm losing you. If I understand correctly, you are using a factory cartridge as a reference for Peak Chamber Pressure not to be exceeded. You are then comparing expansion on your reloads to this reference standard (factory ammo).

1) Brent and I are doing similar with the Strain measurements. We are taking factory loads and using them as a reference standard. Where we differ is that we can use many different factory loads to see how they correlate to the expected Pmax. That appears to be a luxury you do not have since you are tied to a specific brand/lot of brass for your results to be valid. Why is our use of a factory standard invalid where your use is okay?”

HC: Chris, that is an excellent point. I agree we are using the same reference. I stand corrected and agree they are both valid in that respect.

Chris: “2) If you are taking measurements from the first firing of Factory ammo, how do you get around the cited unreliability of expansion on first firing?...

quote:

---

CHE measurements vary considerably on the very first firing of a new case. This is why you do not bother to measure them on the initial firing of the Factory rounds.

---

HC: You simply do not take the CHE measurement on the 1st firing, but the PRE value is valid on the 1st firing. Reread my post on how to do CHE/PRE and I should have stated that there.

Chris: “3) Calibrating with a factory standard has pitfalls. It assumes that factory ammo is safe and near maximum in your barrel. That has proven to be not always the case (see linked thread). There's been a prevalent problem with Federal 223 Match ammo showing severe pressures only in some guns, yet not in others (my strains showed less than SAAMI).”

HC: Excellent point Chris. Fortunately for all of us those situations are the exception rather than the norm.

quote:

---

I’m having trouble with the, “non-issue in practice”, thought process. Any variation in the dimensions of the wall, or a slight skewing of the Strain Gauge placement(from the measurement point) results in changing the data that the M43 provides. Again, it gets back to realizing the data from the M43 can be skewed up or down depending on quite a few inter-related things.

---

Chris: "Your post was in regard to my experience that in spite of the varying barrel thickness under the gauge, the pressures correlated nicely with the expected SAAMI pressures of factory ammo. What can I say? It correlated. You're apparently able to make the leap for PRE and factory ammo. I will say that the attachment and positioning of the gauge is important. Good lamination in crucial and like you mention, any mounting angle introduces a cosine effect that would underestimate the strain measurements (if calibrated theoretically albeit in a consistent fashion). If relative pressures are all you're doing, then even a cosine effect is of no consequence."

HC: Chris, I was not challenging the validity of your experience with what you saw. I was simply saying the placement of a Strain Gauge on a Tapered Surface is something “I would be concerned about” based on my experience with Strain gauges. It has great potential to skew the actual data one way or the other.

But, your point about the “data being relative” anyway, does compensate for it “IF” the person using the Strain Gauges never mentions xxKpsi when discussing a Load. The reason I say that is because it can be misleading to a beginner.

And let me quickly say, I seriously doubt either you, Brent or Jon would ever post something similar to, “ I used xx.xgr of H4350 and a 165gr bullet which produced xxkpsi (M43).”

Let’s say the above had been 55kpsi, some of the beginners would look at a Load Manual, see the MAX psi for that cartridge is 62kpsi and decide that it would be safe to add more powder.

That is not speculation on my part. I’ve read the results of that exact situation happening when I used to visit Shooter.com. The situation resulted when a fool and his M43 posted Loads as if they were infallible. The fool even listed Loads very close to 100Kpsi in his rifle and some of the Rookies over there just dumped them in.

Didn’t mean to get wound up there.

quote:

---

If a person had the resources, it sure would be interesting for someone to attach 3 Strain Gauges side-by-side, around a barrel and hook them to 3 separate Pressure Indicators. If the Strain Gauge theory is accurate, they would all read the same. However, my experience with Strain gauges leads me to believe they would never coincide in value, nor would the “delta value” coincide.

---

Chris: "It's more important that a given gauge give good accuracy (they do) than maintain the consistency from gauge to gauge (they still do as well though). However that is actually an interesting question, not necessarily for your reasons."

HC: "...not necessarily for your reasons." HAHAHA

quote:

---

Chris - Like Brent, I've shot different types of factory ammo to check if the Calculated pressures corresponded to supposed SAAMI spec pressures. Thankfully they did quite nicely...

HC: I sincerely mean, “best of luck to both of you using the Strain Gauge method”.

Please explain how it differs from your calibration with factory ammo? (Assuming my understanding of your use of factory ammo is correct).

---

HC: Good point. I’ll just go on and agree with you that they are the same.

quote:

---

HC: Chris, I respectfully disagree. If the CHE/PRE measurements are taken as I described in my last post, you will be able to see the Expansion Values increase in a linear direction as the amount of Powder is increased in a Test Load. Try it yourself, exactly like I posted it, and you will see what I mean.

---

Chris: "I disagree with your disagreement! The relationship between PRE and charge delta may be linear, but the relationship between charge delta and pressure certainly is not. Therefore, PRE and pressure do not have a linear relationship."

HC: Well, you are actually “partially correct”. It depends on “which part” of the Pressure curve you are working on. With the CHE/PRE Method, you will see a "mostly" linear increase in the Expansion as the Pressure increases, while you are Developing the Load, starting with Minimum loads – up to a specific point. At that time it will begin to level off and no longer be "mostly linear", but you are really beyond where I like to STOP when you get there. (See my CHE/PRE example below.)

quote:

---

Of course, the same is also true for the data taken from the Strain Gauges. By that I mean if you put the same exact Load in 3 cases and the first one measures 55,367psi on the M43, I’d bet neither of the other two loads will measure “exactly” 55,367psi.

---

Chris: "To state that strain measurement should be exactly the same for each firing is a surprising statement coming from you. Velocities for a given load can vary considerably...yet we don't question the chronograph. Rather we work to minimize this variation in the load. An absence of absolute repetition of readings is not a failing of the device but rather in this case an indicator of the variability of the effect."

HC: That is my point exactly. The same thing is true for the values you read measuring CHE/PRE. Your previous post sounded as if you wanted “non-varying” expansion measurements from case-to-case. I completely agree that it just doesn’t work that way, which is the same as the "varying data" provided by the Strain Gauges from shot-to-shot.

...

HC: Showing you some actual CHE/PRE values taken from one of my Data Sheets may be of interest for this discussion. No need to mention the bullet or powder. Factory 223Rem cases in this instance had a Benchmark PRE Average of 0.3762”. I actually worked the Load up with an additional set of Loads between the ones shown, but for brevity I’m omitting them.

Load is 2x.0gr

Before....After...CHE...PRE
0.3728...0.3729...1...0.3749
0.3729...0.3729...0...0.3751
0.3725...0.3725...0...0.3753

Add 0.5gr, Load is now 2x.5gr

Before....After...CHE...PRE
0.3728...0.3728...0...0.3757
0.3728...0.3728...0...0.3760
0.3725...0.3725...0...0.3759

Add 0.5gr, Load is now 2x.0(+1.0)gr

Before....After......CHE...PRE
0.3727...0.3728+....1.5..0.3763
0.3727...0.3728+....1.5..0.3761
0.3724...0.3725......1....0.3766

Interesting to note the last Load is 1.0gr “below” MAX as shown in the Hodgdon and Speer Manuals for that weight bullet. And, all my bullets used in that rifle are Moly coated.

[ 02-06-2003, 03:31: Message edited by: Hot Core ]

I haven't read hardly any of this yet, but my God, you guys are wrighting a book. I guess I'll post another thread to discuss the tips and tricks using the Oehler 43, this one is pretty deep to wade through just to find the tidbits some might be wanting to find or discuss. On with the discussion, looks interesting, if I get a chance to read it soon I'll be tickled.

I actually agree with much of what you�ve said, Hot Core. But I�ll ramble a bit more on the differences....

quote:

---

Originally posted by Hot Core:
HC: Jon, those two paragraphs seem to be in conflict to me. In the first one you say only getting 5-6 reloads per case is OK, but you are concerned about stress on the action.

I want SAFE MAX reloads in my rifles too, but I desire a bit longer case life than you.

---

I didn�t mean those numbers to be absolute. Maybe I should have said, �I don�t care if the cases only last 10 loadings instead of 15.� The point I was trying to make was some brass will last longer than other brass while putting the same amount of stress on the action. So, the life of the brass isn�t my primary concern.

quote:

---

Originally posted by Hot Core:
HC: What method will you use to do that? I understand Magna-fluxing. Is that what you will use?

---

While I may have my bolt Magna-Fluxed or something similar one of these years to test for damage, above I was talking about analyzing the design, coming up with some peak stresses for a given amount of bolt thrust and calculating an expected fatigue life. Maybe this conversation will motivate me to get off my butt and build a Finite Element Model during my lunch breaks.

quote:

---

Originally posted by Hot Core:
HC: I simply disagree. The CHE/PRE Methods have been in use since reloading first began. Their track record is indeed old, but that time span has shown they work extremely well and are totally SAFE.

---

I agree that anybody who follows your methodology will keep himself or herself very safe. But they won�t be any safer than if they properly use a strain gauge. Not too long ago Engineers were using slide rules and doing all their analysis by hand. We simply have much better tools now that give more accurate results. I see no reason to not use them. More accurate results are always desirable.

I suppose I should explain yet another reason I believe using strain gauges is better than your method. It goes a little somethin� like this:

We all agree that a modern bolt action has a large enough margin of safety built in that you aren�t going to blow it up with one round if that round is even anywhere near published maximums. In fact, you could go WAY above them, blow a case to smithereens and the action will not fail. None of us will purposely load that hot so failure of the action�s ultimate strength is a non-issue (except for accidents where powders get switched or there�s something lodged in the barrel, etc but that�s not what we�re talking about).

If an action fails, it will be a fatigue failure. From suffering repeated poundings from really hot loads. What makes a metal part fail in fatigue? Cyclical loading and the number of cycles. An S-N curve will show the expected life of the part given the magnitude of the peak stresses of each cycle. At low stresses the life may be infinite (a very good thing) . At really high stresses the part won�t last very many cycles until it fails.

Where am I going with this?

Well, for a given action, the fatigue life will be dependant upon the PEAK stresses it is subjected to and the number of such rounds fired through it. What�s missing? The duration of each cycle. Within reason, the duration of each peak stress has no noticeable affect on the fatigue life of the part. If the peak lasts 1 ms or 2 ms, it does not matter. One round is one round. Number of rounds and their peak pressures is all that matters.

What does that have to do with anything? Glad you asked....

What you are doing is measuring plastic deformation of a metal. Plastic deformation DOES depend upon the duration of the stress upon it. A simple example would be bending a metal wire. It takes a certain amount of force to bend it to the point it doesn�t spring back. Once you reach that force, the wire will keep bending even if you don�t increase the amount of force you put on it. Put the same amount of force on it for a longer time and it will bend farther. But the peak amount of force you put on it is no higher. Now that�s really simplified but hopefully it gets the point across.

For this reason, more case expansion does not necessarily mean higher peak pressure. Say you have two loads, one with a really fast burning powder and one with a really slow burning powder. Both are loaded to exactly the same peak pressure. The slow burning load will likely have a longer amount of time it spends close to the peak pressure. This will likely expand your cases more than the fast burning load.

So you�ll measure the cases and assume the slow burning load is operating at a higher pressure. You�ll see a higher velocity on the chronograph because it has more area under the pressure curve an you will think this confirms that the load is one of higher pressure so you�ll back it off. In reality, the peak pressure was exactly the same. The load is simply more efficient.

And since the actual peak pressure put on the action was exactly the same, it was exactly as safe to your rifle as the fast burning load. But you back off the powder charge and/or choose the fast burning load because you think the slow burning load is dangerous in some way. You just screwed yourself out of a very good load! The only problem with this load is it will probably wear your brass out slightly quicker than the other load.

And that goes to show exactly what I was saying above�the absolute number of times you can fire your brass is not an accurate measure of safety of your loads.

This is exactly why there is no conversion from CUP to PSI. People ask that question all the time. Shit, we can convert Meters to Yards, Liters to Gallons, Watts to Horsepower, why the heck can�t we convert CUP to PSI? Because two different loads that have exactly the same peak pressure can give very different CUP readings.

The ultimate strength of your action, the load required to blow it to pieces with one shot will have a certain peak pressure. The point at which you are shortening the fatigue life of your action with hot loads will come at a certain peak pressure. Both can be measured in PSI. These are the things that matter to me. CUP simply isn�t as accurate. This is one of the reasons I believe that CUP is already fading off into obsolescence. Now that we have better methods, more accurate methods, CUP is simply the slide rule of pressure measurement.

About all it�s good for is predicting how many loadings you�ll get before you need to buy new cases. In my eyes, measuring case expansion is simply a rather crude approximation of the same principle.

quote:

---

Originally posted by Hot Core:
Some of them would never be able to reload if they had to wait to purchase the $2000 M43 + Laptop.

---

True, but that�s no longer required. For the price of a couple of boxes of bullets you can get set up with these guys:

http://www.fabriquescientific.com/

Doesn�t even require a laptop. Not as fancy as the Oehler stuff, but it will give you accurate relative peak measurements. Like I said, that�s what really matters.

Hey Jon A, You have the very best grasp of Metal Fatigue in a rifle I've seen in print. I encourage you to share that same information with folks that encourage Extreme Loading whenever you see it being posted. It will cause you to receive a bunch of foolish remarks from people who simply don't know better, but some of the Rookies will get the message.

By the way, I agree with darn near everything else you posted.

I've been to the site for the inexpensive Strain Gauge device you mentioned. It is interesting, but I just load to what I consider a SAFE MAX, so I just don't need the hassle.

However, do you know someone who has one of those? If so, how do they like it?

Hey Brent, Didn't mean to skew your Thread from it's original intent.

My apologies to the folk on this thread. I've been tied up with only time to skim posts and no time to add input.

Jon A, thank you for your excellent input. I'd like to add my observations to your assertion that it's the time of max pressure that matters in the stress on the system. Yes, I agree that higher bullet velocites attained with an optimally chosen powder burn rate at a given pressure (versus a faster powder at the same pressure) is evidence of the greater pressure/time AUC of the slower powder.

Until recently I was of the mind of your following quote;

quote:

---

For this reason, more case expansion does not necessarily mean higher peak pressure. Say you have two loads, one with a really fast burning powder and one with a really slow burning powder. Both are loaded to exactly the same peak pressure. The slow burning load will likely have a longer amount of time it spends close to the peak pressure. This will likely expand your cases more than the fast burning load.

So you�ll measure the cases and assume the slow burning load is operating at a higher pressure. You�ll see a higher velocity on the chronograph because it has more area under the pressure curve an you will think this confirms that the load is one of higher pressure so you�ll back it off. In reality, the peak pressure was exactly the same. The load is simply more efficient.

---

However recently in the course of working with the VV 500 series powder, I've found behavior of loads that run counter to that working model.

While working up loads of VVN540 to the same operating pressures (strain measured)of more conventional powders such as Varget and RE15 in our 223/90grJLK loads we've found the following;
1) Considerably higher velocities with N540 at comparable pressure levels. (expected this since the 500 series powders provide a "longer" peak and thus greater AUC.

2) N540 loads showed less battering of the brass, less primer pocket expansion (gauged by the number of reloads the pocket would hold a primer for) and less brass stretch.

Under your model and my previous understanding, situation 2 should actually be the reversed. I was expecting the N540 loads to be much harder on the brass. But some groups are running on their 6th reload without losing a pocket yet, versus an up to 25% loss rate with some of the other powders (yes we've pushed pressures a bit at times).

In fact the N540 results were so counter intuitive, that it was actually disturbing to me (even in the presence of good strain measurements) since I'd always used brass appearance as a safety indicator (more recently secondarily) and N540 would not give that benefit. It might be interesting to see how Hot Core's PRE measurements might correlate to strain and case appearance in this case - I may actually have to pursue that.

Jon A, do you have any thoughts on this seeming paradox?

Hot Core, the Fabrique unit is one of the Strain units I use. It's definitely worth consideration. It's somewhat spartan in comparison to the M43 and per our discussion, it takes some doing to convert Strain units to psi. But bottom line is it works. Problem is that at last word, they were not available.

Hot Core, sensitivity of these units far exceed those of the PRE method. At 50Kpsi, the sensitivity of these units is approximately 0.3% which equates to 150psi. If I'm understanding your method correctly, a range of 0 to 7 ten-thousandths (Waters stops at 5!) yields a measuring tolerance of 14 graduations (standard measuring methodology allows no further interpolation than half a unit), the sensitivity of PRE is approximately 3,600 psi (50k/14). A case could be made for the "floor" actually starting at a higher pressure than 0, thus narrowing the range and increasing the sensitivity, but the problem with PRE is that we don't have any means to determine what that floor is. I don't ask this facetiously; do you know what each ten-thou or half a ten-thou (5 hundred-thou) gives you pressure wise?

That discussion is of course academic since you've acknowleged that you don't care and use PPRE only for relative pressures. But it is indicative of the comparative sensitivities of the PRE method vs Strain.

I do have one practical question. Since using the same lot of brass is essential to not only the validity of the measurements, but also the calibration of your results (versus the factory standard). It appears that you're tied to using brass fired off of that factory standard. Is that to say you're not able to work up loads with factory new brass, or quantities of brass that you were given without any of the parent factory loads? Is there a solution around this?

Brent,
It looks like I missed your question early on; No I haven't correlated bolt lift to pressures. The main use of my Strain Unit has been to work up uncharted loads in an AR15. No stick shift to work - so no bolt lift impressions. However, I pulled this quote off of Ken Waters Pet Loads chapter on his method for judging pressure.

quote:

---

Not to be ignored is a need for increased effort in opening a rifle action and extracting the fired case, or ejecting fired cases from the cylinder of a revolver. A stiff bolt lift or a stubborn lever...is usually reliable, bu tnot entirely - since other misleading factors may at times be present. With revolvers, difficulty in ejecting the empties is a positive sign on borderline pressure....
More positive evidence is the appearance of a shiny spot on the case head opposite the ejector, or a bright ring rubbed around the headstamp area of a case. When it is noted in conjunction with a stiff bolt lieft, this is a sure sign that it's time to stop and back off. While this is a quite positive warning, I prefer an earlier one.

---

[ 02-07-2003, 14:04: Message edited by: Chris F ]

...I forgot to mention that also notably on that Shooters linked thread is Dr Ken Oehler. When you pull up that link, do find by hitting a <control-f> and type in 48352 in the box that pops up. It will "find" Ken Oehler's post in that loooooong thread.

Hot core, of interest to you would be his point #4. Jon A, relevant to my question (consistent with your posting and counter to my observation) is his point #6.

[ 02-07-2003, 15:09: Message edited by: Chris F ]

Chris: "It appears that you're tied to using brass fired off of that factory standard. Is that to say you're not able to work up loads with factory new brass, or quantities of brass that you were given without any of the parent factory loads? Is there a solution around this?"

Hey Chris, This will probably sound a bit off-the wall since you prefer to use numbers that you can relate back to psi, but yes and yes. It a person gains familiarity with CHE/PRE(and ALL the Pressure Indicators considered) you can eventually get skilled enough to be able to develop Loads using new, un-fired cases, without having ever fired a Factory round.

It gets back to your question concerning our discussion about the "mostly linear" PRE as the amount of powder increases. Once you get to a certain point(obviously the actual psi is unknown), the PRE will not expand at the same rate. BUT, this is no way a person just beginning to use CHE/PRE can SAFELY detect the change.

I've been asked in the past to help people who have just bought a Wildcat how to go about this and it is something I refuse to do. If I was there with them, watching ALL the Pressure Indicators and using CHE/PRE, then I could show them first hand. But it is too easy for a person just starting to use CHE/PRE to miss the subtle change.

I've had a lot of 308Win rifles over the years and do not need factory ammo to develop Loads for a new one. On the other hand, I just swapped for a 444Mar and will closely record the PRE measurements as I shoot a box of factory ammo in it to establish a Benchmark.

I thought Shooters.com was shut down. Had a buddy who is following this thread tell me he couldn't get the link to open, but I've not tried it yet. I'll go click on it now.

...

Hey Chris, I got through some of it, but stopped before I got to the end. There are posters in the Thread who some folks think of as Gurus that are not "always" speaking from experience, but lead people to believe they are. I know this because I've communicated with them via email on this subject before.

So, rather than speak bad of them, let me encourage you to base your decisions on what you are able to verify through actual experience for yourself. Everything I've posted is easy for you to check out. But be sure to do it as I posted it, or your results could be skewed.

[ 02-07-2003, 17:43: Message edited by: Hot Core ]

Hot Core -
I tried the link and it appears that section of Shooters is down. A shame. I saved the thread as a pdf file. Problem is it's half a meg in size. Were you able to read Dr Oehler's post? I trust that your criticisms were not leveled at him. I can say confidently that he's "been there, done that" personally.

You are right that I have difficulty with your assertion of not using a reference standard. I do not doubt the sensitivity of your measuremnts, but you earlier criticized the Strain Method for lack of calibration and it appears that you are now saying "we don't need no steekin' calibration!". Please clarify?

Using your 308 Win example, I wonder how well mushy Federal brass PRE correlates to Harder, thicker LC brass?

Try this link R-West posted,
http://talk.shooters.com/room_48/8525.cfm I just downloaded it to read later, it's up to 82 pages now!!

I like Ken Oehlers comment aboy pushing the load till the brass flows and backing off a little, they found them to be "proof" loads most often.

I've not pushed mine that far.....since I got my M43 that is. I've been to maybe 73k psi at most and have only got barely noticable bolt lift resistance 10% of the time at that. God knows how far I've pushed mine in the past, but I am keenly aware that it was higher on many occasion. I had done it enough I wasn't too worried about brass holding up to it though, I always worked up very gradually and still had never even blown a primer. I did blow up an M14 using the wrong powder on the first round once!! Whole nother story there. Thankfull to be here after that one!!! BTW the M43 measured 81k psi on that load, yep, had it hooked up and my laptop was setting about a foot to the right of the reciever. Luckily it was pretty dusty out and I had the top closed down and a bandanna over the top to keep the dust off of it or I might have had shrapnal through the display. Trust me, shit flew everywhere!!!!!!! Gladddddd my off hand wasn't under the clip as I often hold it, or it would be GONE!!!

I'll try to catch up reading this here so I have something intelligent to add.

I'm curious if anyone has worked with the 7.5X55 Swiss rifles and will share/post any information. TIA

I should have included using an Oehler M-43 or some other strain type pressure testing device.

Lonnie, I have not. Sorry.

I have entertained the idea of buying the M43, but this thread just talked me out of it. I do know for a fact that if your cases never reach over the .0007 case head expansion, you'll have a perfectly safe load, never extract hard, case life will be good. I've used this same method for a long time and it works. One of the guys posted that he was more worried about action failure, but you can't have an action failure without the case failure. Of course, you have to be able to use a mike properly, but if you can't do that you probably aren't smart enough to set a powder scale, measure, etc and just should shoot factory ammo.

Well I cought up on all the debate, my brain hurts now!

Jon A: "So explain to me how that can be safer if your loads are nowhere near the pressure levels required to actually fail the brass and you replace the brass frequently."

HC: With the conditions you outline, I agree it is not necessarily Safer. But it is certainly less expensive for a beginner to be able to verify his loads.

Ok....it's not safer now?

1) Brent and I are doing similar with the Strain measurements. We are taking factory loads and using them as a reference standard. Where we differ is that we can use many different factory loads to see how they correlate to the expected Pmax. That appears to be a luxury you do not have since you are tied to a specific brand/lot of brass for your results to be valid. Why is our use of a factory standard invalid where your use is okay?�

HC: Chris, that is an excellent point. I agree we are using the same reference. I stand corrected and agree they are both valid in that respect.

What do you mean by, they are "both" valid?

Please don't take this personal HotCore...You have made assertions and not even had any experience with the strain setups to base it on, bear this in mind.

You're leading people to believe the PRE method is SAFER and MORE ACCURATE is not even true and can in no way be substantiated at all, by you or anyone. It does have some merit, as we all know.

The strain gage setups are very sensitive and will RELIABLY interprete stretch in steel to such a high degree of accuracy IT REALLY works. It is calibrated for use on steel and so are the gages to a much higher degree than any case expansion measurement technique you could use, even if you could use an optical comparitor!! As you say the case is the weak link. Yes the case is the weak link in your whole ARGUMENT. If it was as consistant as the barrel steel you'd have something, but it isn't and never will be, period. The data the Oehler computes is designed and based on real testing with serious accuracy equipment. PRE is only relative to the case itself, which properties are most inconsistant, unlike barrel steel, which is why it's basically all but been abandon.

You cannot even compare the two methods in any reasonable terms whatsoever, it's ridiculous to even try, although you make an admireable effort at doing so. What you have here is that you are comparing case stretch based on something that can't be reliable for so many reasons it should obvious.

What is driving me nuts about this is I think you know the strains is more accurate than PRE, you have to, I've listened to you long enough to know you're not anywhere remotely close to being dumb, It seems you don't want to accept it because it costs too much or something?? For cryin out loud, do you think people put this much effort into developing something that "just by coincidence" tells me factory ammo in every rifle I've shot to date hasn't exceeded SAAMI maximum average specs??? Almost all the time it's just below max average to top it off. You're trying to tell me the numbers are wrong? How wrong are they then? You cannot know either, but I'll lay money on my Oehler 43 when hooked up side by side with a Piezo transducer that you'll not be even close OR CONSISTANT and mine is within 5k psi every time? After this you'd maybe have something to base yours on and you would still not be close the next batch you tried either. I've run enough ammo through mine to KNOW all factory ammo doesn't vary and the rifles are predictable beyond belief. You see this equipment was designed WITH psi equipment and calibrated with such as well. The variables such as brass, chamber walls, taper, you name it on these is so unimportant if the gage is applied smoothly, bonded well, measured and placed correctly, it's a no brainer... It's all relative to the factory loads psi. in that barrel tested in. It doesn't matter if I get 40k psi readings or 70k with the selected factory loads, they are not over SAAMI max average and you'd know how far off it was one way or the other, make sense??? We are measuring a CONSTANT, not a VARIABLE as you are in PRE. The accuracy of my Oehler is consistant with everything I've tested and corralates to book loads, factory ammo, you name it. Buy one then give us your EDUCATED opinion on how inaccurate it is. In all sincerity, I guarantee you that you'd be back to correct YOURSELF on this. Without doing just this, how much should anyone value your opinion on "this"? Seriously......

I'm not buying the bit about putting the gage on either, It's so damn simple I could have my son doing the next one with some instruction and not think twice about it. CLEAN, ETCH, NEUTRALIZE, STICK THE TAPE TO THE GAGE, APPLY ECCELERATOR TAPE ON BARREL, PULL BACK TAPE, TWO DROPS GLUE ON THE EDGE AND SQUEEGIE OVER AND HOLD 1 MIN. How hard is that to do???? Measuring all done of course...

Chris: "Your post was in regard to my experience that in spite of the varying barrel thickness under the gauge, the pressures correlated nicely with the expected SAAMI pressures of factory ammo. What can I say? It correlated. You're apparently able to make the leap for PRE and factory ammo. I will say that the attachment and positioning of the gauge is important. Good lamination in crucial and like you mention, any mounting angle introduces a cosine effect that would underestimate the strain measurements (if calibrated theoretically albeit in a consistent fashion). If relative pressures are all you're doing, then even a cosine effect is of no consequence."

HC: Chris, I was not challenging the validity of your experience with what you saw. I was simply saying the placement of a Strain Gauge on a Tapered Surface is something �I would be concerned about� based on my experience with Strain gauges. It has great potential to skew the actual data one way or the other.

What experience do you have with them? Spelling is gage BTW, strain gage is spelled differently than dial gauge. Don't ask me why????

But, your point about the �data being relative� anyway, does compensate for it �IF� the person using the Strain Gauges never mentions xxKpsi when discussing a Load. The reason I say that is because it can be misleading to a beginner.

And let me quickly say, I seriously doubt either you, Brent or Jon would ever post something similar to, � I used xx.xgr of H4350 and a 165gr bullet which produced xxkpsi (M43).�

Let�s say the above had been 55kpsi, some of the beginners would look at a Load Manual, see the MAX psi for that cartridge is 62kpsi and decide that it would be safe to add more powder.

That is not speculation on my part. I�ve read the results of that exact situation happening when I used to visit Shooter.com. The situation resulted when a fool and his M43 posted Loads as if they were infallible. The fool even listed Loads very close to 100Kpsi in his rifle and some of the Rookies over there just dumped them in.

Explain to me how I'm responsible for someone not working up a load to reasonably safe psi in their own gun, that's like saying gun MFG's should be held responsible for giving instrucion on how to load the cylinder on a revolver when you shoot someone with it????

Hodgdon lists loads on the can, rag mags contain load data, reloading 101 says WORK up!!!!!

You want to take liberty to do and load as you will, I'm not a control freak... God gave us all choices in life. God also gave us a brain too. The ONLY thing I'll do is say start low! You don't want to give your load data that's your perogitive.



Start low and work up!

quote:

Chris - Like Brent, I've shot different types of factory ammo to check if the Calculated pressures corresponded to supposed SAAMI spec pressures. Thankfully they did quite nicely...

HC: I sincerely mean, �best of luck to both of you using the Strain Gauge method�.

Please explain how it differs from your calibration with factory ammo? (Assuming my understanding of your use of factory ammo is correct).

HC: Good point. I�ll just go on and agree with you that they are the same.

You're still dealing with the weak link ARGUEMENT here. The cases are the inconsistant variable link, barrel steel is not is predictable, expansion is measurable and repeatable to the degree brass never will be and therefore steel is a constant. The only variable is psi itself, the gage is constant and calibrated also.

HC: Chris, I respectfully disagree. If the CHE/PRE measurements are taken as I described in my last post, you will be able to see the Expansion Values increase in a linear direction as the amount of Powder is increased in a Test Load. Try it yourself, exactly like I posted it, and you will see what I mean.

Chris: "I disagree with your disagreement! The relationship between PRE and charge delta may be linear, but the relationship between charge delta and pressure certainly is not. Therefore, PRE and pressure do not have a linear relationship."

HC: Well, you are actually �partially correct�. It depends on �which part� of the Pressure curve you are working on. With the CHE/PRE Method, you will see a "mostly" linear increase in the Expansion as the Pressure increases, while you are Developing the Load, starting with Minimum loads � up to a specific point. At that time it will begin to level off and no longer be "mostly linear", but you are really beyond where I like to STOP when you get there. (See my CHE/PRE example below.)


What part of the pressure curve you're working on?

What point does what level off? that's just it, there are no specific points or anything specific about this method that has anything to put your finger on. Your statement is so vague, how is this more accurate than the strain device again?? You really lost me here. No doubt this means something to you but it is so primitive and subjective in every way I don't understand how you make some of the statements you do???

Of course, the same is also true for the data taken from the Strain Gauges. By that I mean if you put the same exact Load in 3 cases and the first one measures 55,367psi on the M43, I�d bet neither of the other two loads will measure �exactly� 55,367psi.

Chris: "To state that strain measurement should be exactly the same for each firing is a surprising statement coming from you. Velocities for a given load can vary considerably...yet we don't question the chronograph. Rather we work to minimize this variation in the load. An absence of absolute repetition of readings is not a failing of the device but rather in this case an indicator of the variability of the effect."

HC: That is my point exactly. The same thing is true for the values you read measuring CHE/PRE. Your previous post sounded as if you wanted �non-varying� expansion measurements from case-to-case. I completely agree that it just doesn�t work that way, which is the same as the "varying data" provided by the Strain Gauges from shot-to-shot.

With PRE there is very high potential that the brass itself is falsly indicating varying psi when in all likely reallity psi is too stable for the PRE measurement to even pick up the difference. It simply isn't even sensitive enough to do this like the strain can. What is the resolution of your method?

Jon A, do you have any thoughts on this seeming paradox?

Hot Core, the Fabrique unit is one of the Strain units I use. It's definitely worth consideration. It's somewhat spartan in comparison to the M43 and per our discussion, it takes some doing to convert Strain units to psi. But bottom line is it works. Problem is that at last word, they were not available.

Hot Core, sensitivity of these units far exceed those of the PRE method. At 50Kpsi, the sensitivity of these units is approximately 0.3% which equates to 150psi. If I'm understanding your method correctly, a range of 0 to 7 ten-thousandths (Waters stops at 5!) yields a measuring tolerance of 14 graduations (standard measuring methodology allows no further interpolation than half a unit), the sensitivity of PRE is approximately 3,600 psi (50k/14). A case could be made for the "floor" actually starting at a higher pressure than 0, thus narrowing the range and increasing the sensitivity, but the problem with PRE is that we don't have any means to determine what that floor is. I don't ask this facetiously; do you know what each ten-thou or half a ten-thou (5 hundred-thou) gives you pressure wise?

That discussion is of course academic since you've acknowleged that you don't care and use PPRE only for relative pressures. But it is indicative of the comparative sensitivities of the PRE method vs Strain.

If you don't want to spend much money on one the one Chris recomends is only 2 or 300 bucks and will give you an eye opener as to the new technology advancements availible to us today, and for quite some time now I might add.

If you all get anything from this, understand that brass is a very poor "gauge" because of it's many inherant variables, it work hardens, in the area of the PRE point it thins as well, hence the seperation point. This is possibly the worst place for consistant expansion measurements over many cycles especially if you FL size. Hardness of brass varies from piece to piece and lot to lot, which means shot to shot also. Waters and most stop at .005" PRE, HotCore .007" so how this is reconciled is likely HotCore using factory loads to determine hardness of brass at factory PSI's to get to know his expensive brass. If one dare use bulk brass and have no benchmark and it happens to be a "hard" lot you'll push psi too high, maybe. If this psi happens to cycle too long at a certain point you will be risking fatigue in the steel as John gave a detailed account of, the knee curve it's commonly refered to. A point where an infinate number of cycles at factory psi are obtained is completely comprimised at a psi point where the number of cycles fall like a rock and you stand a chance of firing your last round! Cases will fail and actions handle sudden stress and explosions, but weaken one over repetitive high psi loads and it no longer has the strength to contain a perfectly good case that never even let go....THE ACTION JUST WILL NOW!!!

Take care,

ChrisF: "You are right that I have difficulty with your assertion of not using a reference standard. I do not doubt the sensitivity of your measuremnts, but you earlier criticized the Strain Method for lack of calibration and it appears that you are now saying "we don't need no steekin' calibration!". Please clarify?"

HC: Chris, I've answered this before and agreed with you that we are using the same reference.

ChrisF: "Using your 308 Win example, I wonder how well mushy Federal brass PRE correlates to Harder, thicker LC brass?"

HC: I don't remember well enough to quote from the top of my head. I have used some of the LC and I do remember the PRE varied much more than the Fed, Win and Rem cases.

But, the LC cases I had were from mixed Lots, so any inference that they were "bad" from my data would be misleading.

...

Hey Brent, I copied your post and will respond to it when I have time.

[ 02-08-2003, 17:06: Message edited by: Hot Core ]

jstevens,

One of the guys posted that he was more worried about action failure, but you can't have an action failure without the case failure.

Not true at all, case failure is managed by the action on slight to severe sudden overloads that can happen for one reason or another. In the case of an M14 I blew up it was the wrong powder. What the action is NOT ment to handle is loads that don't blow the case but are high enough to cause fatigue and finally let go. This could be 1 round, 10, 50, 100, 500, or whatever fired at the repetitave high psi, the higher the psi the fewer cycles needed to cause action failure. 5k psi could take you from an infinate number of cycles to just several thousand, another 3k psi could reduce that to LESS that hundreds.

This is the main problem with buying used rifles of unknown origan. If they have been subjected to repeated overloads, you could be the UNLUCKY winner, and with a normal load at that!!

Proof loads are usually 40% or more psi higher than factory, and one is shot in each rifle before leaving the factory. Repeated proof loads will blow a rifle up! And they don't blow primers either. I'd reconsider and take a closer look at the M43, you'll be happy you did. It isn't $2000 either, it's half that. The laptop I bought is basically my new desktop PC, just traded in. I'll never own a desktop again, besides the couch is alot more comfortable than settin at the desk.

I have decided to build my own. I have Lab View software and am going to buy a strain gauge receiver module (2 channel) and set it up for a full bridge gauge. A friend of mine who is in the engineering program has the power supply put together and is putting together the board right now. Nice and compact. My laptop will sit on top of it. Now all I have to do (along with so many other things) is to wait 'till this summer for $295 for the module. Then I'll be cookin' with grease.

I hav ebuilt my own strain gage sytem with a home made mplifier and a digital storage oscilloscope because Oehler charge 25% more for export price

there is another way to get pressure informations that is the Kolbe P MAX made by Border barrel this systm work with bullet acceleration

check www.http://www.border-barrels.com/
you doesnt need to glue anything and that far faster than the strain gage but that doesn t give you the curve , just the max pressure.

good shooting

DAN TEC

Brent: “What do you mean by, they are "both" valid?”

HC: Come on Brent, If I have to explain the meaning of the word “valid”, then this discussion is not going to get too far.

Brent: “Please don't take this personal HotCore...You have made assertions and not even had any experience with the strain setups to base it on, bear this in mind.”

HC: I’ve got 30 years experience with Strain Gauges in various Manufacturing organizations. I agree my experience was not in using a M43, but a Strain Gauge is a Strain Gauge. One big difference (after reading your entire post) is the Strain Gauge devices I have experience with “actually detected small high pressure changes”.

Brent: “You're leading people to believe the PRE method is SAFER and MORE ACCURATE is not even true and can in no way be substantiated at all, by you or anyone. It does have some merit, as we all know.”

HC: The CHE/PRE methods have been around since before even your Father was born. They are time-proven, accurate Methods which allow a beginning reloader(or experienced reloader) to Develop(from below) SAFE MAX Loads. To argue the point is to argue with reloading history.

Of course it can be substantiated. All a person has to do is either borrow a set of 0.0001” capable Micrometers, or spend $21 to get them from www.wideners.com keep good Data Sheets and follow the CHE/PRE Method I outlined above.

From all most every post I’ve ever bothered to read on the M43, the person using it eventually starts quoting psi values well above those considered SAFE by SAAMI. Why they do this is beyond rational thinking and can mislead the beginners or get themselves hurt. Anyone desiring to blow themselves up just need to do it somewhere other than “next to me” at the Range. When I see a guy break out a M43, I ALWAYS give him plenty of space and try to stand directly behind him when I’m not shooting. That doesn’t mean “you” are unsafe, cause I don’t know you. Only relating what I’ve observed firsthand.

NOTHING is SAFER than duplicating what the Factory Loads establish as a Benchmark and you can do that easily with CHE/PRE. If you want to spend $2000 to do accomplish something similar, help yourself. I just won’t spend my money that way.

Brent: “The strain gage setups are very sensitive and will RELIABLY interprete stretch in steel to such a high degree of accuracy IT REALLY works. It is calibrated for use on steel and so are the gages to a much higher degree than any case expansion measurement technique you could use,…”

HC: Brent, you’ve written this as if “you” have experience using CHE/PRE. I find that difficult to accept since, if you had that experience, you would not make such a statement.

Brent: “For cryin out loud, do you think people put this much effort into developing something that "just by coincidence" tells me factory ammo in every rifle I've shot to date hasn't exceeded SAAMI maximum average specs??? Almost all the time it's just below max average to top it off. You're trying to tell me the numbers are wrong?”

HC: Somewhere in a post above I saw you talking about going to 73kpsi with some Loads. That is the largest DANGER I see with people who use the Strain Gauge devices. A person calibrates with a cartridge that might be at 50kpsi or 62kpsi. Where ever it really is they don’t know, but they think they do. Then they decide to go on and run Loads at say 73kpsi(per Brent’s example). If the original Factory Load was at 50kpsi then there might not be any harm. But if it is at the upper end of SAFE Pressure and “the M43 user mistakenly thought” it was at say 10kpsi lower, then when they go to 73kpsi, they may really be at 83kpsi.

Brent: “It doesn't matter if I get 40k psi readings or 70k with the selected factory loads, they are not over SAAMI max average and you'd know how far off it was one way or the other, make sense???”

HC: Well no, it makes no sense(to me) at all that you would say you can get 40kpsi  70kpsi and you would know how far off it is one way or the other. It appears you are “assuming” the Factory Ammo you use to do the calibration with is “ALWAYS” at a specific Pressure Level. That just isn’t the way it works. Factory Ammo Pressure varies depending upon the “specific blend” of non-canister grade powders they are using to achieve their goals. Granted it will AVERAGE below SAAMI MAX, but it certainly is not at some specific Pressure from Lot-to-Lot or Manufacturer-to-Manufacturer.

Brent: “We are measuring a CONSTANT, not a VARIABLE as you are in PRE. The accuracy of my Oehler is consistant with everything I've tested and corralates to book loads, factory ammo, you name it.”

HC: Brent, I totally disagree that you are measuring a constant. Strain Gauges (that in fact are accurate) would indicate not only variations between Lots of ammo, but variation from shot to shot. Apparently the M43 is even LESS ACCURATE than I originally thought.

Brent: “Buy one then give us your EDUCATED opinion on how inaccurate it is. In all sincerity, I guarantee you that you'd be back to correct YOURSELF on this. Without doing just this, how much should anyone value your opinion on "this"? Seriously......”

HC: I appreciate your offer to help me spend my money, but I’ll pass. We(pre-M43 reloaders) got along without a M43 for many, many years and loaded literally millions of rounds of absolutely SAFE MAX ammo. People who base their impression on my experience(as well as Ken Waters, Bob Hagel, etc.) with the CHE/PRE Method (as I outlined it above) will understand I know what I’m talking about. And it will save them $1979 ($2000 - $21) in the process.

Brent: “Spelling is gage BTW, strain gage is spelled differently than dial gauge.”

HC: Gauge and gage are interchangeable in some contexts. Reference: Webster’s Seventh New Collegiate Dictionary, copyright 1965. Prior to correcting someone else’s spelling, you would be wise to proof read your own posts. (I noticed at least 8 misspellings in the portions of your post I’ve included here. I don’t claim to be a great speller, but I would be if I could measure the words accuracy with a 0.0001” capable Micrometer though! HA)

Brent: “Explain to me how I'm responsible for someone not working up a load to reasonably safe psi in their own gun, that's like saying gun MFG's should be held responsible for giving instrucion”

HC: First off, do you mean “instruction”? HA Anyway, I didn’t say “you” are responsible for someone not working up a Load responsibly. What I said is ANYONE stating xxkpsi in with a Load posted on the net “can” mislead a beginner into thinking “since it worked for that guy, surely it will work for me”. What works well in one firearm does not necessarily work well or SAFELY in another firearm.

You can see it all the time on the various Boards where some beginner will post, “Need a HOT Load for a 300DoDah!” People with the best of intentions respond with Loads that work for them in their rifles and the “beginner”(the guy making the original post) often just takes off loading whatever he sees as the MAX. The when someone posts xxkpsi (M43) with his load, the beginner is fooled into thinking it has more validity so working up is a waste of time. Then they have the potential to get into serious Pressure Problems.

Brent: “Start low and work up!

HC: Well Brent, you finally got one thing right. HA

Brent: “1. What part of the pressure curve you're working on? … 2. What point does what level off?”

HC: 1. Working on the part “below” the SAAMI MAX as established by the factory ammo. 2. It will begin leveling off at a point above SAFE MAX. You basically do a “Trend Analysis” as you watch your data with an eye out for a lower increase in PRE. This is not something a person can do without some experience using this Method. But if the beginners stick to the outlined Method, they won’t get this far.

Brent: “that's just it, there are no specific points or anything specific about this method that has anything to put your finger on. Your statement is so vague, how is this more accurate than the strain device again?? You really lost me here. No doubt this means something to you but it is so primitive and subjective in every way I don't understand how you make some of the statements you do???”

HC: It is because I’m “speaking from experience with CHE/PRE”. It appears you’ve just not tried it, but still choose to criticize it. If you did try it, I’ll predict you would learn a great deal about your Loads.

But, Chris and I’ve put the “more accurate than” portion to bed. I suspect you just overlooked it in the previous posts.

Brent: “With PRE there is very high potential that the brass itself is falsly indicating varying psi when in all likely reallity psi is too stable for the PRE measurement to even pick up the difference. It simply isn't even sensitive enough to do this like the strain can. What is the resolution of your method?”

HC: PRE indicates variability because it exists from shot-to-shot. Where ever you are getting the impression that psi from shot-to-shot is totally stable is completely WRONG. That is simple Handloading 101 as someone else posted.

But, I base that on over 4 decades of experience using CHE/PRE and 30 years experience with extremely accurate Strain Gauge(spelled correctly by the way) equipment. If in fact the M43 indicates you are getting the exact same psi from shot-to-shot, then something is seriously wrong with the M43. Or if it is working per spec, then it is even less accurate than I’d imagined.

Brent: “If you don't want to spend much money on one the one Chris recomends is only 2 or 300 bucks and will give you an eye opener as to the new technology advancements availible to us today, and for quite some time now I might add.”

HC: I believe my eyes were just opened when you said, “psi is too stable for the PRE measurement to even pick up the difference.”, and by that I do mean your assumption is TOTALLY WRONG. So, I sure don’t need to spend any money on a device that is that inaccurate or misleading when my good old Micrometers work perfectly.

…

Hey Brent, I’m getting the impression from your last post (that I just responded to) that you are getting “upset, emotional and/or thinking I’m taking shots at you”. That was not my “intent”, but I can hand it out as good as I get it if need be.

CHE/PRE works well to develop good accurate SAFE MAX Loads. We’ve done so for years and years and the old methods don’t become obsolete simply because there is a more expensive way to accomplish a similar end goal – SAFE MAX Loads.

This is my next to last post to this thread. I’ve beaten my points to death and we are beginning to repeat them.

Best of luck to all you Strain Gauge folks!