The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Re: More About PressureTraceGo | New | Find | Notify | Tools | Reply | |
| Re: More About PressureTrace | Login/Join |
| one of us |
Steve, Looks like I was posting at the same time, little slower though.  I wonder what load name I sent you that you made that plot from, do you remember? Take a look at the screen shot I posted below yours there, it really matches up with Quickload well, the one I sent you, hmmmm.... RL25 that much faster? See if you have that load, I'd like to have a look at it again. I've got so many of them to look through, and I'd like to compare the one you plotted to the one PT plotted... | ||
|
| one of us |
Anyone use one of these babies? Looks like a very economical way to go, vs >$1k for the Oehler. I know the Oehler will do lots more stuff, but if all you're interested in is pressure data, are they comparable? | |||
|
| one of us |
For $20 you can buy a strain gage (high accuracy). For $750 you can by an amplifier/conditioner/read-out. For $3 you can buy superglue. For $2 you can buy nail polish remover. For free you can do the math. I assume you have a lap top, or other portable computer with a printer port. All the electonics can be had from Omega. This will get you into an accuracu range of +/- 5% on pressures. You can set the sampling rate at 1 milliseconds and get a real good pressure trace from any position on your barrel. Of course you will need a lap top computer for the data acquisition. Have you seen the lap top in the background on some of my pics, ever wonder what it is for? Scott | |||
|
| one of us |
I have one, and I have a ball with it. The one difference of opinion I have with the manufacturer is that I put my gages on the bottom of the barrel, under the stock, and make sure that any stock pressure at that point is relieved. I have two rifles instrumented, one a 30-06 which I hunt with, and the other a Finnish M39, for which there is little good reloading data. I plan to add gages to my 308 and my Swedish Mauser. It's simple to use, and it works great. I've done the math to find out how repeatable it is, and it is better than most published piezo PSI data. As nearly as I can tell, from looking at sources of error, the absolute accuracy is within a percent or so. | |||
|
| one of us |
Quote: I call that MANLY. | |||
|
| one of us |
Quote: Hey Bwana-be, The short answer is - All the Strain Gauge Devices sold to people outside an actual Ballistics Lab are a serious waste of money. 1. In order for them to work with any amount of reliable accuracy, they would have to be "Calibrated" and you can't do that because you can't buy "SAAMI Calibration Ammo". That alone blows them out of the water. I see Denton in this thread and if you ask him about "Calibration", you end up getting a "Set-Up Procedure" which has nothing to do with actual Calibration. Keep pushing the issue and he will eventually say you can "Self-Calibrate" the Gauges with repetative measurements. Basically - you just guess at what the value is a whole bunch of times and then say it must be calibrated! Feel free to quote me on, "HAHA HAHA HA". 2. For the average person to get an "accurate" measurement of the chamber wall thickness to the "actual degree necessary" is also pure speculation. 3. And you have to "glue" Strain Gauges to your barrels. HA They really make the rifle user friendly - not! But they will drive the "Resale/Trade Value WAY DOWN" when someone notices them or the spots where you had them. Quote: 4. You also need to include the cost of a Laptop to drive the Oehler, so the real cost is $2000-$3000 depending on what you get. 5. They are very comparable in that they also can't be calibrated, you also can't get accurate chamber wall thicknesses, and they drive the value of the firearm in the ground. ... If you want real "useable" Pressure Information, invest $21 in a set of RCBS 0.0001" capable Micrometers and learn about Case Head Expansion(CHE) and Pressure Ring Expansion(PRE). Denton has been trying to prove these methods are not reliable and apparently has had no luck at all doing it. Of course, he can't because they work so well. ... Here would be my recommendations: 1. Develop your Loads using the never improved upon Creighton Audette Method. 2. Don't waste money on a chronograph and for absolutely sure not on any Strain Gauge devices. 3. Buy a set of 0.0001" capable Micrometers and learn about CHE & PRE. 4. Since any Pressures derived from the Strain Gauges are nothing but pure speculation, just look at the Load you are testing in a Hodgdon Manual and the listed Pressure Info will be "as accurate" and very possibly "more accurate" than anything you would get from a Strain Gauge as far as "useable information". 5. Spend the money on reloading components that you would have TOTALLY WASTED on the Strain Gauges or even on a Chronograph. Gets lots of Trigger Time at multiple distances and you will be way ahead of anyone doing otherwise. Probably not what you wanted to hear, but that is the reality of the issue. | |||
|
one of us |
Bwana, The RSI strain gage is a very good way to go. The beauty of this particular gage/system is you can remove the gage from the barrel with acetone anytime you want. That is the reason I instrumented my .500 A-Sq., .300 Ultra and a .375 H&H. I have no data yet since the .500 kept yanking the gage and pigtail apart. The .300 wasn't assembled until a little bit ago and it is too dogone cold outside right now to go shoot the .375. I can shoot, but the laptop won't last that long.  | |||
|
one of us |
I can't agree with Hot Core's condemnation of the method. For one thing, you can use factory cartridges to set a maximum strain for your particular rifle. This strain will not equal the maximum allowed for your rifle since factory ammo is loaded below maximums. As for the "SAAMI Calibration Ammo", I believe it only gives SAAMI max pressures when fired in a SAAMI spec pressure barrel, and most factory barrels aren't so tight as this -- in short, so what if you can't buy such ammo? From the descriptions of CHE I've read, Ken Water's seems typical, and he uses the deformation from factory rounds to calibrate pressure as well. Without factory rounds, I don't see how to calibrate this method, either, unless it is a wildcat operating at the same pressure as the cartridge providing the parent case and you know the CHE for the parent cartridge. Yes, there are errors in measuring the ID and OD at the point where the gauge is applied. I believe it would be on the order of a percent or two if you use a decent micrometer and a decent set of gauge pins. From the equation for strain vs. pressure, it seems obvious this won't be show-stopper. Frankly, I suspect the strain gauge is more accurate than CHE if you're looking at a cartridge for which no factory ammo exists. Finally, Lyman's 47th reloading book gives a table with fps, psi, CUP, and case head expansion measured for a 10 shot string of the same load. It is seen that fps tracks psi more faithfully than either CUP or CHE (and CHE was the least accurate). I still think one of the better load books (data taken in a pressure barrel) backed up with a chronograph is safer than CHE. Karl | |||
|
| one of us |
I can't agree with much of anything Hot Core said in that post. The case head expansion method has been proven to be practically useless time and time again by the major ballistics labs. Even from the most basic 9th grade science perspective you can see it's useless because there's no reference standard to compare expanded cases to. For this method to hold any validity you'd have to have a lab test a few cases from the same lot of brass you're using to get a standard expansion vs. pressure. Even then, brass is too hard to provide a reliable standard. | |||
|
| one of us |
Quote: Hey Karl, In #1., since the "Pressure" varies from Lot to Lot from the same manufacturer and also from manufacturer to manufacturer, how do you use Factory Ammo to establish the "Calibration Pressure"? How do you know it is not at a MAX Pressure Level? If it is below MAX, what Pressure is it? 2. The reason SAAMI Calibration Ammo is absolutely necessary is because it is the industry recognized "Calibration Standard". Here is how it really works in a recognized ballistics Lab: You buy Calibration Cartridges from SAAMI to determine the Benchmark Pressure Standard for your specific Test Barrels, whether they are SAAMI Minimum Chambers or randomly selected production rifles. Lets say as an Example the SAAMI Calibration Ammo is specified to read 60kpsi in a particular cartridge. You shoot it in your Test Barrel and get 55kpsi on your Strain Gauges(redundancy being very important), then that is the MAX Pressure ALLOWABLE when developing Loads in that barrel for that cartridge. Or you get the 60kpsi, or 68kpsi - it dosen't matter cause whatever that Strain Gauge reading happens to be, it says that is the MAX Pressure ALLOWABLE in that specific barrel based on SAAMI Calibration Ammo. As we follow this line of thinking, it is now obvious to see why it is dangerous and foolish for anyone(outside a Lab) who has a Strain Gauge device, to list Loads and the "Pressure" they generated because the information is not accurate and is misleading to people who really don't understand that that information is based on "ZERO" Calibration to a known Standard. Quote: 3. Absolutely. Here a Factory Cartridge is used to establish a Benchmark Standard for Expansion BUT in no case is it used to say what a "specific Pressure" happens to be. All it does is say that when you Load your Test Loads in factory cases from this Lot, stay at or below that amount of Expansion. 4. Actually, with experience using CHE and PRE, you can tell when to STOP adding Powder in Wildcats. It becomes obvious with experience when using the methods. Quote: 5. Karl, it is nice to agree with you on one point - Yes indeed, there are "errors" in trying to read the chamber's wall thickness. Using Gauge Pins inside a "Tapered Chamber" has the potential to get "errors". Few people outside a manufacturing environment have the financial resources to afford the proper CAD/CAM device necessary to get this "critical measurement" at an accurate, reliable level. I disagree that is is OK to justify using "guessed at measurements" by saying it seems obvious it won't be a show-stopper., when in fact an error in determining the Chamber Wall thickness will eliminate the possibility of getting accurate Strain Gauge information. ... Karl, now how is it you use a completely Unknown Pressure Value (Factory Ammo) to "Calibrate" a Strain Gauge device? If there is some way to do it, I'd sure be interested in knowing how it is done. | |||
|
| one of us |
Quote: Hey boltman, History proves your thoughts to be in error. 1. For many years, CHE, PRE, the various Visual Pressure Indicators, and C.U.P. devices were used together to allow the Ammunition Factories and the Component Manufacturers to establish SAFE MAX Loads. If you will pick up a Speer Manual, you will notice the method is still explained how any new reloader can use CHE to their advantage. 2. Here you use Factory Ammo to establish a "Benchmark Standard" for your CHE & PRE. It does not tell you what the Pressure was in the Factory Ammo, but it does tell you that if you stay at or below those values, you will be at a SAFE Pressure Level. 3. Actually, the information a Lab would provide to you would be fairly worthless. They can't determine how much "Expansion" will occur in your specific firearm with the ammo, only what occurred in their Test Barrels. They could provide an "Average Pressure", but since the actual "Pressure Value" is not used in CHE & PRE it isn't useful. 4. Always nice to end on a positive note. Here you are partially correct. CHE & PRE are only really useful on the first 6-9 Loads in a set of cases. This varies depending on the intensity of the Loads being tested. ... CHE & PRE have been used ever since "Self Contained Cartridges" were first created. They have worked very well for over 100 years and will continue to do so long into the future. In fact, they are the SAFEST, most accurate Pressure detection methods a Reloader outside a Lab has access too. | |||
|
| one of us |
Hot Core, I agree with you 110%, with regard to calibration, in particular, and the usefulness of the equipment when non-calibrated, in general. With the very best strain gage, signal conditioner, and data acquisition card money can buy, coupled with accurate OD and ID barrel measurements (which aren't at all easy to acquire) you will still realize a 10% - 12% error on all your pressure measurements. With the cheapo equipment, which I assume Oehler (or they are given the equipment away for free) sells in their system, you have a measurement system accuracy of between 15% and 20%. It ALL depends greatly upon the strain gage and the amplifier/conditioner accuracy. This stuff is just like stereos, you have to pay for the accurate equipment, if you are happy with "noise" that comes relatively cheap. With regard to what the error IS. The error exists between the measured valued and the actual value. The measured value can be VERY VERY consistent from measurement event to measurement event, it is just not the ACTUAL value, and there is where the problem lies. Could be high could be low. This is why Oehler tells you to test factory loads to acquire a MAXIMUM safe limit! They have no calibration, so this is their methodology to make sure that they compensate for the measurement system errors and your errors in measuring the barrel OD, ID and axial position fore to aft on the barrel shank. Yes, you must place the strain gage directly on top of where you made the ID and OD dimensional measurements, and the OD and ID MUST be measured in the same TRANSVERSE PLANE of the barrel shank.. One last little issue with these systems in general. As the wall thickness of the barrel increases (OD-ID)/2, the accuracy of the strain gage decreases rapidly. This is, due to the fact, that there is less and less deflection occurring so the measurement is getting smaller and smaller. Since the error of the system is FIXED, with the smaller measure recorded, due to the thicker barrel, the overall percentage of the measured value which is error is increased. In other words, the measurement error increases exponentially (sort of) as the barrel wall increases. The technical term for this phenomenon is SENSITIVITY. BTW, nail polish remover works very well at dissolving super glue, which is used to secure the strain gage. It leaves no marks that cannot be easily repaired. In reality, without calibration, you are only getting a pressure number, which is no more accurate, than the pressure number provided by most internal ballistics programs. The ballistic programs are ~ 15% the cost though! Pressure calculations on most internal ballistics programs are ~ 20% accurate, which is what the Oehler system will give you in a non-calibrated form with a sporter weight barrel. These is the facts, if you cannot handle them, I feel sorry for you. For the record, well calibrated strain gage measurement systems, utilizing the most accurate signal conditioning and data acquistion equipment, and with proper sensitivity (wall thickness) can obtain accuracies of less than 1% error, measured value versus actual value. Scott | |||
|
| one of us |
Hot Core - hello it's been awhile. I need to correct one part of your previous thread in regards to denton not being able to prove his research. Back in October we went a few rounds about how accurate CHE (PRE) was in relationship to a strain gauge. You were asked to measure cases and take part in this - you refused. I ask denton to mail me the cases to measure, and I failed miserably. (denton - I have both batches of cases and all my measurements). I am the hold up with his research - due to forces beyond my control that I would rather never have to deal with again. This "test" only faltered, it did not fail and as of Monday will continue to move forward. Keep an open mind in regards to the outcome, I'm willing to bet I can name which shells will be subjected to high pressure(as confirmed by a strain gauge which I am many miles away from). denton - I appologize for the major setback, you already know what started it. Hot Core - no one has failed to prove anything with the exception of myself. Don't rule out strain gauges as an accurate measurement of pressure - time will tell. | |||
|
| one of us |
Now Hot Core, cool down there fella. Go back and read my post. I didn't say factory ammo would give you a calibrated pressure. I said it would give you a strain limit to use in developing your loads. This is no different than using factory ammo to set the CHE limit in your preferred method. Yes, my idea to use gauge pins wasn't well thought out. It would be better to rely on the chamber drawing to pick ID. If your gun conforms to the SAAMI spec for the chamber, the error in the ID should be under 1%. For instance, in the small cased .223, the diameter near the shoulder is .354" and the spec allows for a .002 deviation, or 0.5%. As for my "it seems obvious" comment, it was based on looking at the equation relating strain to pressure and putting in a few % error for ID and OD. The error in pressure is about double that of the error in the OD and ID measurements. ScottS, I must agree with your estimate (facts?) that a basic strain gauge system might produce an error of 15 to 20% error from the "true" pressure. That's why I suggested using factory ammo to set a stain limit. That many cheap signal conditioning circuits are not too stable I've seen where I work. Still, 15 to 20% is better than the 100% error I've seen reported when CHE is compared to piezo. Me, I don't own a stain gauge rig. For a cartridge for which no reliable load data exists, I use an unproven mix of QuickLOAD and load book data to estimate what the possible fps might be. I then set a target fps of 5% below my estimate and use my chronograph.Karl | |||
|
| one of us |
Hot Core, did we wake you from your nap? Sorry about that. Think about this for a moment: We measure electrical current very accurately. But how did the first person to make a calibrated ammeter calibrate it? He didn't get to just make up arbitrary units. The Ampere was already defined. What he did was run a constant current through an electroplating solution, for a certain time, and weigh the amount of material electroplated out. From Coulomb's Law, he knew that current is directly proportional to the amount of material plated out per unit time, and he knew the constant of proportionality for the material used. So he indirectly calibrated the new ammeter to known constants and to weight, which he could easily get. It was the only alternative, because no direct standard existed. Such indirect calibration is very common, and perfectly sound. The error in a strain gauge reading is just the cumulative error of the input variables: The physical properties of steel, the OD of the barrel, the ID of the barrel, the gage factor of the strain gage, the properties and thickness of brass, and the gain of the amplifier. Most of these can easily be had to three signficant figures, without excessive difficulty. Modern gage amplifiers are extremely good. 10-12%?? Egad! Not with any decent stuff designed in the past three decades. I am particularly fond of the Burr-Brown INA128, which is an $8 chip with truly phenominal stability and precision. Gain is completely determined by a single resistor, and it is so temperature stable that the error is negligibly small. Surprise! The CUP system is strictly a relative system and is not calibrated to anything. Piezo transducers used for pressure measurement are indirectly calibrated, just as strain gages are. And Barnes Bullets uses strain gages to generate their load data. And Dr. Lloyd Brownell, who wrote one of the most respected volumes on rifle pressures used strain gages. So stow the crappola about strain gauges not working, and not giving accurate results. They work extremely well. Deal with it. I put my strain gages under the stock, where nobody can even see them. If you picked up my '06, you'd have a hard time telling that it is instrumented, unless I told you exactly where to look. So quit spreading crappola about strain gages destroying the resale value of a firearm. It just ain't so. If you carefully read the appropriate article in the article on page 92 of the July, 2003 issue of The Varmint Hunter, you'll see that the strain gage system provides measurements at least as repeatable as commpercial piezo systems, and that have very respectable absolute calibration. Until, and unless, you do an equally thorough and rigorous experiment and analysis, you have no basis for your statements. | |||
|
| one of us |
Hey Bwana-be, This is one of the beauties of the shooting world. Ain't all the varied responses great? Are we thoroughly confused yet? A few days ago I opened (wrote?) my big mouth and lent my self proclaimed semi-expertise and experience, and boy, EVERYBODY had a different viewpoint! So in that spirit... I do agree with much that has been said in support of AND critical of virtually all the methods discussed in the prior postings. But, (here I go sticking my neck out) a combination of the methods discussed will generally give an even better chance at understanding what your particular firearm/load is doing. The one thing lacking--the piezo method is the RELATIVELY most accurate (I can already hear everbody sharpening their keyboards in preparation to shred that statement). The key word here is relatively. I had the opportunity to see pressure curve graphs for three different cartridges generated by the Remington ballistics folks using piezo equipped pressure barrels and was TOLD that this was the the best stuff they had--RELATIVELY (I only know what I was told). But, they also use many of the other methods discussed above to help corroborate their data. The Remington generated pressure graphs measured the curve to much finer degree (in time) and sensitivity (in pressure variation). I was surprised at how much the pressure curve varied as it increased to peak pressure and decreased to bullet exit. There were up and down variations along the way as much as 10,000 psi ! One common theme in the prior postings: they mostly agree the methods don't give us the ACTUAL pressure, instead it gives us an idea based on a somewhat artificial benchmark we establish (using any of the prior discussed methods). To some degree or other they can all be useful. I have had almost unlimited access to a Oheler Ballistics Lab for years and at one time access to two different Oehler Labs for a while--they gave different pressure readings/curves in the identical rifle and load! This not a knock on Oehler, I suspect the RSI equipment is similar. Instead it shows there is a degree of error going on--but the same goes for every other method available to us. I think either the Oehler or RSI would give a person more info to use as a tool. Of course you must invest not only money, but be prepared to invest lots of time time into setting things up correctly and figuring out just how useful/accurate the data really is. These days I just mic my case heads and be done with it--it gives me a safety baseline. If the bullet is getting the kind of velocity I want (ES and fps) and hitting my aiming point consistently I'm fairly satisfied. Don't get me wrong, internal, external, and terminal ballistics is fascinating stuff, and any knowledge can be helpful--it's just that there is such a diversity of experiences, conclusions and opinions, I have decided that internal ballistics is still one short step away from voodoo. BTW-nail polish remover is diluted, scented lacquer thinner (AKA-Meythel Ethyl Ketone), and acetone is a "hotter" version of lacquer thinner. It is not the solvent that occasionally mars the bluing or stainless, it is the epoxy that does it. Casey | |||
|
| one of us |
Hey ScottS, I do believe we are in agreement. Nice post. Quote: Hey Karl, Just keep "implying I am a "little" fellow and you could get me Hot.  I'm just a few biscuits shy of 300 pounds, so leaving "BIG" out by default implies "little". Actually, your sentence would be a bit more accurate to read, "there BIG fella."  Quote: Well..., duuuhh..., you certainly are correct! I did misread your statement and now that you got my attention by beating me over the head with it, I can clearly see what you actually posted was different than what managed to sink through on my end. I'm still of the opinion that attempting Calibration with an "Unknown" is foolish, but what you stated is different than "claiming" the System is in Calibration. You are saying a person should use Factory Ammo to establish a Benchmark Standard (whatever it may read on the Strain Gauges) and those non-calibrated Pressure values should not be exceeded. Well, yes I can TOTALLY Agree with that. In fact Karl, let me say that your idea is perhaps the very first "rational statement" I've ever read on how a person could use a relatively expensive Strain Gauge System to some advantage. Good for you. Quote: Karl, could you give a few more details on this statement. I don't want to chance disagreeing with you until I completely understand what you are saying. Where have you seen a 100% CHE Error compared to Piezo and what were the circumstances? | |||
|
| one of us |
Quote: Well, well, well, another Vote in the "Strain Gauges Systems Aren't Perfect" column. And another Vote in the "CHE works fine" column as well. Hey Casey, Have you tried Pressure Ring Expansion(PRE)? ... Hey Denton, For the life of me I can't understand "why" you think an article you wrote for Varmit Hunter would have any influence on my opinion. I lost confidence in your "knowledge" when you didn't know the difference between "Calibration" and a (questionable) "Set-Up Procedure". I just don't have any faith in your Strain Gauge "Worship" and the totally irrational posts you make in an attempt to support them. Due to many years of dealing with Strain Gauge Systems, I seriously believe I've forgotten more about Strain Gauges than you will ever be able to rationally comprehend. And I see no benefit in "arguing" with you. But, best of luck to you. | |||
|
| one of us |
Here goes--You take a factory case, fire and measure CHE, you are setting the benchmark for that particular run of brass, when you reload.Other brass may be different ductility.My wildcat 458He built from 450NE brass, the Bertram ones I had would easily get over a 100 fps(60k load) more than the Bell brass and show no measurable expansion.Same load with Bell I had would loosen primer in one shot.Now the vaiations in base ductility affects the CHE system much more than minute differences in the case side thickness half way to the shoulder where a strain gage is taking the readings.Getting accurate thickness measurements of case sides , barrel thickness, barrel diameter,metal strength, etc is just measurement science and applying that info to formulas for radial stress, that have worked for years is very accurate.Some mention thick barrel would not expand as much so there would be a bigger chance of error, but you would make the sensor bigger and on a heavy barrel actually get more accurate readings as barrel vibrates less.If I use gage and chrono, and check & make adjustments with my Velocity formula in reverse, that gage can be operated within 4%,Ie 2000 psi plus or minus in the 50k range.Load to load differences are more than that.Ed. | |||
|
| one of us |
Hot Core, you continue to humiliate yourself. And you don't even seem to know it. How sad. Nobody has said that strain gages are perfect. All I have said is that they are as good as any system we have, and neither of the other two are perfect. Still, they are useful. To the best of my knowledge, nobody has ever done a formal investigation that shows that either PRE or CHE work at all. If you have data, we'd love to see it. Until, and unless you do an experiment and analysis as rigorous and complete as the one I did, you have no basis for your comments. We're supposed to believe you because.... why? You say so? Well, isn't that special? Would you like to dig deep into your "20 years of experience with strain gages" and try my quiz again? Last time, you scored 0 out of 5. Anyone with real knowledge can answer all the questions in about 10 seconds apiece. You failed completely, but tried to bluff your way through on one question with a totally wrong answer that I exposed with quotes from the recognized text on the subject. Would you like to try that again? Please just do this one for us: A strain gage with gage factor G is in a series circuit with a stable resistor of value equal. 10 volts are applied to the series string. The gage is applied to a cylindrical chamber, and pressure is applied inside the chamber. The diameter of the chamber is 1" at rest. Under pressure, the chamber expands so that its circumference under the gage is .005" greater than it was at rest. What is the resulting voltage change at the junction of the gage and the fixed resistor? | |||
|
| one of us |
Hi T/C. It's good to hear from you. I hope things are settling down satisfactorily for you. As I said, take care of first things first. If it takes a little while to get to the experiment, the cases will still be there. When circumstances permit, we'll finish up our experiment. If PRE or CHE work, we will be able to say so. If they don't, we'll say that. Let the data decide. | |||
|
| one of us |
Hot Core, my notes have scribblings from an article written by Barsness in the 10/02 Handloader. He measured CHE on cases after they were fired in a piezo rig. He settled on a CHE of 0.0005" for the high pressure cases, but he noted what value to use is difficult to pin down. He found one cartridge where CHE could at times run as high as 0.00125" at safe pressures, a 150% error. My claim that CHE can be off 100% was, then, misleading. The CHE was off by that much, but not in the direction of underestimating pressure. Barsness felt that CHE tended to overestimate pressure. CHE could not in anyway be used to estimate the actual pressure; it was far too non-linear. My notes also have a quote from Ken Howell (former editor of Handloader) saying "Tests by a number of experimenters have shown that typical pet loads developed by the traditional methods, including miking cases, usually develop maximum pressures in the proof-load range." Proof loads are 30-40% above the nominal limit, and that is a big error, in the unsafe direction. OK, denton, the electronics I've dealt with didn't have the luxury of B-B chips, so maybe the electronics can be better than I expect for the price. That RSI rig is very inexpensive, considering the hardware and the software involved. It's been a long time since I worked with strain gauges, in school. It recall they are a bit temperature sensitive, and barrels do tend to heat up. Is this handled in the conditioning electronics or do modern gauges have temperature compensation? Lastly, denton, I can't agree with the statement "The CUP system is strictly a relative system and is not calibrated to anything." I believe the crushers are calibrated, but only in static tests. The very rapid changes in pressure during firing is, I believe, what causes CUP to miss the true pressure. And then there's the problems of sticky anvils, etc. I'm not sure how one would actually verify what the true pressure is in a sporter with an RSI rig attached. Perhaps you could use the components specified in a proper load book, and then vary the charge to get the correct fps on the chronograph. The pressure should be pretty close, then, to that shown in the load book. Anyone tried that? Karl | |||
|
| one of us |
asdf.. Yes, the RSI rig is quite inexpensive. There really isn't much in it. It's just a strain gage amplifier, using a different chip than the B-B, and a microP with an A/D converter and an RS232 interface. As nearly as I can tell, the really serious work is in the circuit layout, to prevent random RFI, and in the software, both of which are far from trivial. The RSI unit has considerably less random error than the earlier Fabrique unit, which isn't a bad unit. I am amazed at how good some of these chips are, especially considering the price. Your use of the word "luxury" is right on. It's soooooo much easier than it used to be. Can you imagine trying to get that kind of performance out of a box of 12AT7's? Can't be done. Yes, strain gages are slightly temperature sensitive. From FYBO cold to really uncomfortably hot, the difference amounts to about 250 PSI, which is small enough to make little difference. The curve is well known for each model of gage, and you get a graph of it (linear) with each box of gages. It's easy to compensate for, if you want to include it as a factor. I prefer to simply slap a thermocouple on my barrel, just forward of the receiver, and do my testing at constant temperature. The RSI does re-zero the bridge automatically before taking a new reading. The statement about CUP being a purely relative system is from Dr. Brownell's book, "Firearms Pressure Factors". It set me back for a few minutes when I read it, because it is kind of a strong statement. But it is true. Originally, investigators thought that the copper crusher system produced data in PSI. If you read Ackley, he had a copper crusher system, and reported his results as PSI. Well, of course, it turned out that this belief was wrong. The copper crusher system is fairly repeatable, but it does not produce an output directly in any basic engineering units. You cannot, for example compute bolt thrust directly from CUP numbers, as you can from PSI numbers. There are cases with very fast powder where the copper (or lead) pellet cannot respond to the peak pressure, and you do get significant error. Hodgdon confirmed to me that they definitely had to "reel in" some early shotgun data, once they got better instrumentation. All my work has been with rifles, and I've done the math to ensure that this is a small source of error in that case. In rifles, the pellet does have sufficient time to respond. I have done the research and math to be able to state that the RSI system is at least as repeatable as commercially published reloading data. Refining an estimate for absolute calibration error involves estimating the variances of the random errors associated with the input variables to the equation: physical properties of steel, ID, OD, etc. That's a lot of work. Since all of input variables are fairly easily obtained to three significant figures, it's a very safe bet that calibration error isn't a lot more than a percent or so. That's as good as the calibration on a commercial piezo system. (Now you see that statistician coming out... in physics, you try to be perfectly accurate under all circumstances. In statistics, it's good enough to just be really, really close. Don't spend any time developing a number that is more precise than you need for decision making.) Actually, piezo systems are typically terribly temperature sensitive. Anything that is piezoelectric is also automatically pyroelectric as well. Hope this adequately answers your questions. | |||
|
| one of us |
Quote: Hey T/C nimrod, Yes, it has been awhile. And yes, I did reject the offer to be included in the "Test", because of two things: 1. It would be a total waste of "my time", since I already know the outcome from well over 4 decades of using CHE/PRE properly. 2. From what I saw you all post as the Test Method you will be following, you are going about it "wrong", so there is no chance for CHE/PRE to work properly. Don't be too hard on yourself, in the long run none of this matters, life comes along and throws mountains in front of all of us. | |||
|
| one of us |
Quote: Hey Karl, I do remember that article. At that time I was thinking it would have been nice for one of the old Pros like Ken Waters or Bob Hagel to have taken Barsness aside and show him how to use CHE properly. I'll "guess" the reason for the gross errors he got on CHE was because he did not measure across the Casehead in the same exact spot "Before Firing" and then again "After Firing". There is also another "wrong way" to go about it. And that is to take multiple CHE readings on a single case "After Firing" and average them. The only proper way to insure a correct reading is to measure the Casehead prior to Firing in one specific spot (say directly opposite the "P" in R-P), record that measurement to 0.xxxx", fire the case, remeasure across the "P", record that value as 0.yyyy", then subtract getting 0.000z" CHE. Additionally, no one to my knowledge has ever said or even suggested a person can base CHE on the results of only one case. It should be taken using one Load on at least three cases from the same Lot and 4-5 if practicle. At that point, you would "Average" the CHE and compare it to the original (average) Benchmark Standard CHE derived from a box of factory ammo (10-20 cartridges). And of coures, PRE is totally different. You measure it only "After Firing" and you do rotate the Case until you locate the "high spot" on the Pressure Ring. Then you record that data and compare that PRE directly to the (average) Benchmark Standard PRE. In either method, measuring CHE/PRE should only be done for 6-9 reloads which varies due to the intensity of those specific reloads. After that point, the Cases "work-harden" and the CHE/PRE values are suspect. If the Primer Pockets are still snug, they can still be used for regular shooting practice. And, the reloader must either Full Length Resize(FLR) or Partial-Full Length Resize(P-FLR) in order for the Pressure Ring to be reformed back into the Casewall between Firings while doing PRE measurements. Quote: I remember back when Ken Howell was one of my "Heros". Back a few years ago he signed on to HuntAmerica and I really looked forward to his "wisdom" for the Rookies. After watching "howl" trash the Rookies asking him for information, his creating the "howl CARET Factor" (howl Complicating Any Relatively Easy Task), and his incessant propensity to talk bad about dead people in a self-aggrandizing manner, I no longer have any use for his opinions. In fact, in the quote you mention above, it includes one of howl's trademark "sideways trashings" directed toward the Grand Master Reloading Guru Ken Waters. It is apparent you have read a good bit of Handloader. Can you see where howl is making an attempt to trash Ken Waters? ... The bottom line is, everything I've posted about CHE/PRE is verifiable by anyone who has a set of 0.0001" capable Micrometers. People who believe otherwise can quickly see the benefits of using CHE/PRE for about $21 (www.wideners.com RCBS 0.0001" capable Micrometers), a pencil and a sheet of paper. But, they must follow the proper CHE Procedure and the proper PRE Procedure, not just take off doing random non-sequential measurements in the wrong place. | |||
|
| one of us |
Quote: So you're not willing to give the readers on this board the benefit of your vast experience? Not willing to expose your technique to scrutiny? Chicken. Actually, since you refused to participate, it will be kind of nice when the results come in. You will have no standing to criticize if PRE and CHE are debunked, or to receive glory if they are sustained as good measurement systems. | |||
|
one of us |
Just an observation from the peanut gallery, but.... If John Barnsness (who might not be the tallest peg in the board, but he's no dummy by any means) can't figure out how to properly mike cases.... then I suggest that it is not a feasable method for amateur investigators. We also know that professional investigators (i.e, ballistic labs) cannot use it, do no use it, and recommend against anyone else useing it...... If this method is not suitable for even advanced amateurs, and unusable for professionals...... ......why are we even talking about it? JMO, Dutch. | |||
|
| one of us |
Dutch, All of these methods should not be attempted/relied upon, by the amateur! One must understand what the heck they are doing if they are to acquire ANY useful data, even with the strain gages (maybe especially with the strain gages). From what I have read on this thread I really don't think to many here should be using any of these systems/methods. They do not seem to have the knowledge/training/experience to understand the limitations of the method and/or instrumentation. I see lots of magazine/sales catalog/book readin' and very little actual field experience. Some of the statements are extremely contradictary to the Corporate knowledge of SEVERAL major corporations; however, these statements fit nicely into some sales brochures I have read. Enough wasted bandwidth, for me anyway. Scott | |||
|
| new member |
As both Denton and asdf have pointed out, PressureTrace really is quite inexpensive to buy given it's functionality. About a year and a half was spent in the circuit design, firmware and software. (Since it's my company, I get to decide to expend that kind of effort for a product that is inexpensive enough for most shooters to buy.) However, don't make the mistake of thinking the components themselves are cheap. The four layer circuit board costs quite a bit more to make and the Analog Devices Instrumentation Amp and A to D converter don't come cheap either. Even the Op Amps are a more expensive variety. There's just no way to make a 741 work. Believe me, I tried. RFI was a major problem with early prototypes and drove the requirement for a four layer board with very careful circuit layout. It's also the reason that a special (read expensive) cable is used for the strain gage input line. Once RFI was under control the really difficult pieces of the firmware and software were finalized. As I've mentioned to a couple folks, the devil is in the firmware. Just for reference: -PressureTrace captures data at twice the (claimed) rate of the Oehler unit. Once triggered it takes a reading once every ten microseconds for 2.5 milliseconds. -False triggering is reduced by implementation of firmware similar to a circular buffer. The signal must rise above the trigger level, and stay there, for half a millisecond. -Before every shot the unit resets the baseline (zero strain) level to take into account barrel expansion due to heating. | |||
|
| new member |
I posted about the circuits in PressureTrace earlier. But, then I got thinking about this thread and some other discussions on pressure. I decided that some "higher level" discussion might be in order, as PressureTrace isn't just a tool for indicating peak pressure. (As a matter of fact, the peak pressure readout almost wasn't put into the product.) PressureTrace is a diagnostic tool. A little background. Southwest Products created and manufacturers PressureTrace. RSI did have substantial design input and they are currently the only dealer. The genesis of PressureTrace was a discussion about chamber pressures and all the factors that go into the pressure a cartridge generates. We came to the conclusion that a better, more affordable pressure system could be made specifically for serious accuracy reloaders. A system that would allow them to fine tune their loads and pick correct powder/bullet combinations; not just tell them that they had high pressure. The PressureTrace system calculates pressures using both thick and thin wall calculations (thick wall for the barrel, thin wall for the brass). This differs from other sytems which require a general pressure adjustment factor for what the brass will hold. Like the others we also recommend the system be calibrated against a load of known pressure (primarily as a safety precaution) but for round barrels with gages over the mid point of the main case body, usually no correction is required. When no data is available (wildcat), PressureTrace will produce extremely reliable pressure readings. It is designed to accurately measure pressures developed in working rifles and does not attempt to extrapolate SAAMI tight chamber pressures. PressureTrace uses a much faster processor to collect more data points. This means larger plots can be overlayed so even slight changes to pressure can be detected...at any point along the pressure curve. The software does not "smooth" the curves so what you see is what is happening in your chamber. This makes PressureTrace a superior load development diagnostic tool. Even slight changes to neck tension, seating depth, barrel fouling, etc. can be detected in the plots. Even if they're not evident in the peak pressure readings. The higher sample rate also allows PressureTrace to pick up secondary pressure spikes of extremely short duration that are not evident with other systems. As has been proven by studies performed by Denton and another lab, PressureTrace's peak pressure readings compare favorably with both SAAMI systems and the 43P; with typically less error then other systems. Back near the beginning of this post I mentioned that at one time during early development we considered NOT providing peak pressure readings with this system. We have always felt peak pressure was at best a secondary benefit to PressureTrace. It's real benefit is the ability to show minute changes to the pressure curve's shape. The area under the pressure curve is what translates to velocity and reloaders have a high degree of control over the curve's shape. The "classic" shape of an efficient and forgiving load that performs well in a wide range of conditions cannot be determined by peak pressure alone. | |||
|
| one of us |
And you don't have to be a genius to use it. Glue the strain gage in place, let it cure 24 hours, put a battery in the interface unit, load the software, plug it in, turn it on, and start taking data. | |||
|
| one of us |
Quote: Hey Dutch, I also appreciate "some" of Barsness writing. My experience has shown he is correct on more than he is wrong. But I do occasionally find things he writes to be different than what I've witnessed first-hand. I don't doubt he sees the things he writes about, but some of his experience has led him to the wrong conclusions more than once. Concerning difficult things to do, I'll site one example. If someone asked you to go out and change the UHF Radio in an RF-4B, an EA-6A, or an EF-10B(all now retired), you might indeed have trouble doing it with everything setting right in front of you. But, if someone handed you an Instruction Manual, you should be able to do it. Now, I base your "being able ot do it" using the Instruction Manual because I saw lots of young fellows with a High School education have the ability. And you are obviously smarter than a whole bunch of them. As to using CHE/PRE, I'd bet "you" could use it if you followed the directions in my last post. There is nothing tricky or complicated about it once you know and follow the proper procedure. | |||
|
| one of us |
Quote: Hey Burt, Nice write up concerning your System. Two questions, where does a person outside a Ballistics Lab purchase "a load of known pressure"? Is where to buy it in your Instructions? | |||
|
| one of us |
Quote: Until and unless you take the time to read the answer already given, I don't know why anyone would bother giving you a new one. By your feeble and perverted definition of "calibration", the balance scale you use to weigh powder is of no use, because it cannot be calibrated. Not calibratable? How can that be? Don't we check it with standard weights? No. It is impossible to make a standard weight. You can only make a standard mass, which, for convenience, you might mark with its weight at a particular place. But it is truly a standard mass, not a standard weight. It will weigh .5% more at the poles than it will at the equator. So your scale is useless, because there are no standard weights to calibrate it. You must give up weighing powder, because the readings are meaningless, mere conjecture, useless. At least according to your definition. In truth, the scale is very useful, even though there are no 100, 200, or 500 grain standard weights to calibrate it with. Gravity varies only slightly over the Earth's surface, so the approximation we get by calibrating to standard masses, and multiplying by g to get force due to gravity (weight) is more than acceptable for reloading purposes. If you rule out indirect calibration, you have also ruled out your balance scale. If you rule out systems that have no absolute calibration, but only give relative measurements, you have ruled out the CUP system that was the standard for many decades. | |||
|
| one of us |
Quote: For me there are always two questions for pressure measurement: 1) What is the calculated accuracy, given the long chain back to the national bureau of standards? 2) What will be done with the pressure measurement, given the silliness of SAAMI specs and the individuality of each gun? We might task 100 handloaders on the internet to work up until there was a .001" growth in the extractor groove, while using the same caliber, bullet, and powder. We might task different 100 handloaders on the internet to measure the pressure of median of the above found load. IMHO, the deviation in the two groups would probably be about the same. Does that make measuring pressure as good as measuring brass? No. It is not, because there is still the big error, what to do with the pressure measurement. The next task for the two groups is to reduce the load until it is reliable enough for hunting, and record that load. IMHO, we will see the pressure testing group show a comparatively huge deviation in this step compared to those reading the brass. -- A society that teaches evolution as fact will breed a generation of atheists that will destroy the society. It is Darwinian. | |||
|
| one of us |
Excuse me please, I find the discussion a bit too much focussed on one aspect which is,IMHO, not the major important one for the use of pressure curve meter. If I want to develop loads, I find I do not need a pressure test device. There are enough signs for the limit: flat primers, hard bolt extraction, case head measurement. The information I get is only static= max pressure (as with CUP). If I want to know how a powder or a primer performs, how a heavier bullet, seating depth or crimp affects pressure development, I cannot imagine of anything but a pressure tester like the PressureTrace as it performs a dynamic reading, i.e. a pressure curve. Even if one uses the factory setting without calibrating it, one gets an answer to above questions when one studies the deviation of the pressure curve from the reference load (relative reading). When you feel you need absolute readings, buy a pack of factory ammo (you'll mostly find how much pressure they develop). In addition, you may have a ballistcs lab test your reference load with your rifle. This doesn't cost that much. Now you calibrate the test device and you can compare the results with data from your reloading books or whatever you want to find out. | |||
|
| new member |
Wouldn't it be useful to use Pressure Trace in conjunction with other "BRASS" checking methods ONCE. Find the pressure where you exhibit signs of strees in the case, primer, etc. Now, when you decide to work with a different lot of brass, powder, bullet weight, ogive, etc. you should have a pretty good idea of where to stop. Pressure Trace will tell me MY pressure in MY rifle, and it may or may not be able to predict what your pressure will be in your rifle, however, if you shoot one of my "KNOWN" loads, I could probably predict where you will end up with your MAX. load. IMO, it just makes sense to have multiple tools in ones toolbox,afterall it is hard to build a house with JUST a hammer! edge. | |||
|
| one of us |
Quote:Quote: Hey Burt, I'm guessing you are still "looking" for the answers? Take your time, I'm still interested. | |||
|
| one of us |
Quote: Hey Burt, You REALLY SURE you want to tie onto denton for "credibility"??? The reason I ask is because the more I read his posts, the farther from reality he gets. Basically using him as a reference for your product doesn't seem to speak real well for it. From your "reference boy" denton: Quote: Thinking denton "might be right" and that I might have missed the answers, I did go back and re-re-re-re-read the post you made. Can't find a thing that answers the questions, "where does a person outside a Ballistics Lab purchase "a load of known pressure"? Is where to buy it in your Instructions?" Gotta believe I got "dentonized - AGAIN". (dentonized = TOTALLY FALSE, WRONG and MISLEADING INFO that a person actually believed, coming from denton) Fortunately, he can't fool me on ANY of the technically inaccurate loonacy he posts. Anyway, not trying to give you a hard time at all Burt. Just want to know about the "known pressure ammo" so I can buy some if I wanted to. ... And Burt, now here is a classic example of denton's "Quality Engineering/Management knowledge???": Quote: So, I flip open a handy phone book. Well, low and behold, there are all kinds of folks who can not only Calibrate a scale,but they can also Certify the Calibration to the NBS. For those of you who think denton was correct(you have been dentonized ), here are three numbers selected at random from a Louisville, KY phone book simply because I noticed they had "800" numbers. You can call them and ask, "Can you Calibrate and Certify a Scale?"When they say, "Why, yes indeed podner, we sure can!", then you can set back in your chair and say, "Well, old Hot Core told me I got dentonized!" American Scale 800-928-5005 Jack Mann Scales 800-333-6833 Premier Scales 800-320-0421 Hey, don't feel tooooooo bad about being dentonized, I used to think he knew something of worth about Strain Gauge Devices until I asked a him few questions. | |||
|
| one of us |
Quote: Hey edge, First off, "Welcome Aboard AccurateReloading". I see this is your first post. I think that is an excellent idea. In fact, I've been trying to get it done ever since the first person on old "Shooters" had a M43. Never could get him to understand that you couldn't get useable PRE data if you "Neck Size" the cases. From the rest of your post, it reads as if you do have a Strain gauge Device. Would you be willing to run a non-biased comparison if I gave you specific Instructions on how to perform the CHE/PRE testing? No interference from me or anyone else during your Testing. Let the chips fall where they may. All correspondence would be through this Board so everyone can see what is being done and discussed as it happens. In addition to your Strain gauge Device, you would need a 0.0001" capable Micrometer and a set of Full Length Resizing Dies. Caliber of your choosing that has a SAAMI Pressure in the 50kpsi or above range. The reason I specify that Pressure, is because CHE will not work on some of the old "Low Pressure" cartridges, but PRE will work on Low or High Pressure. Only real problem I see would be getting "known Pressure ammo" to Calibrate your Strain Gauge Device! | |||
|
| Powered by Social Strata | Page 1 2 |
 | Please Wait. Your request is being processed... |
|
The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Re: More About PressureTrace
Visit our on-line store for AR Memorabilia