To get off of the whole CHE-PRE discussion I have some questions about a chrony.. I see alot of guys say velocity is the WAY to measure.. I know I love my chrony and ouldnt work up loads without it.. Because in my eyes thats only the way to see what is actually goin on without hundreds of dollars for more advanced equipment.. But you still cant say for sure your readings from your chrony is letting you no you have to much pressure.. For instance lets say this your workin up a load for a 243 87grainers with a 22" bbl. We use IMR-4831 and book max says 40grains will give 3200fps in a 24"bbl(not actually data just numbers off the top of my head) lets say @ 39grains we get a avg 3075 fps and @ 40grs. we also get a avg of 3075.. Now is 40 grains max pressure becouse it didnt gain any velocity??? I would say this is kind of a grey area.. My question is is it to much presure or not enough bbl to get to 3200fps?? After all we are using a 22" bbl and not a 24" bbl that is in the book.. I do agree that there is no need to run 40grains if you are getting the same with the lighter charge but my point is in the exp velocity doesnt = pressure.. Now on the other hand lets say @ 39grains we are getting 3160 and @ 40 we are getting 3300.. Now this I would say there is TO much pressure since you are getting way faster speeds then what the 24" bbl was getting.. But lets say there is NO other signs of high pressure.. I would still back off alittle bit becouse something isnt right..

What if @ 38 grains we get sticky bolt or other signs of pressure but your velocity isnt where book says it is??

Now lets say you have a wildcat with very little data or just loads and no velocity data.. How can you tell your at max pressure?? You have nothing to compair with except similiar calibers.. You can go with eratic velocity changes when working up loads like 39gr gives 3000fps and 40 gives 3300 fps or get to the point where you dont gain any velocity at all.. But what if you dont have any instances like this? How do you know what is to fast and how can you tell weather you have to much pressure?? Im gussin that sooner or later you will get eratic readings? Or you will get some other sign of pressure..

Guess my whole point is you need to use ALL the tools/signs together becouse 1 by itself is usless..

6.5 Bandit

6.5 Bandit, if you have no data, a good computer simulator will be your best friend, combined with a chronograph.

Between a (free) Powley calculator and a $64 chrony, you would, in the real world, be able to get within 95% of optimum with little or no risk to you or your firearm.

There are numerous examples we can bring into this discussion. We could start by inviting OKshooter to share some of his PRE vs. Strain gauge data for the 30-06 manual he published......

We could evaluate WHY benchresters can fire 10+ rounds through a case at 70,000 plus PSI, and not get ANY case head expansion......

FWIW, Dutch.

Hot Core,

My conclusions concerning PRE and CHE are based on the very same logic you've used to discount strain type measurements continually, BUT the errors in your method are FAR AND BEYOND that encountered with strain systems. A "combined" source of errors in strain gage usage, such as an incorrect case wall thickness, incorrect case to chamber wall clearance, differences in rise time, virgin vs fireformed brass etc, etc will reproduce relative PSI numbers that probably vary in peak PSI by no more than 3-5K PSI at the most. Now look at PRE and it's resolution capabilities, even when ALL controlable variables are eliminate and everything is measured as close as humanly possible, the two don't even begin to compare to having the same resolution.

When have you EVER tested CHE and PRE against a Piezo transducer system to even say you KNOW the same PRE expansion measurements equal the same pressure with factory ammo and your handloads???? I would guess never, because I'll bet we'd of heard all about it many times over if you had... You will however see data in reloading manuals being used to tell you what min and max load levels are and what their MV's were using factory barreled rifles, barrel length and all, NOT SAAMI TEST BARRELS, strain systems are used for most of these tests, not PRE or CHE, or Piezo transducers... Why do you think that is? I'm going to venture out and say, that strain measurements are not only a means of comparing relative pressure, but a very reasonably accurate method of indicating actual peak pressure in YOUR barrel, and well within the same varying range of what Piezo transducer measurements would be had you drilled a hole in your barrel and installed one next to a strain gage.

If you don't like a wire coming your gun connected to a computer, don't use one, or wait for a wireless model to come out.... There is a glue on Terminal pad that provides a larger copper contact area away from the gage to solder/unsolder the wire so that it's only on there while testing is being done. I am using these now, and the gage and Terminal Pad are kept hidden under the barrel on most of my rifles.

6.5 Bandit,

To get the best indications from a chrono, I believe the barrel needs to be long enough to burn all the powder you've selected, or like you said the pressure will still build and MV may not.

I wouldn't say one tool by itself is useless at all, but more "could" be helpfull.

Now lets say you have a wildcat with very little data or just loads and no velocity data.. How can you tell your at max pressure??

I've got two wildcats I've been testing. One thing I've obsevered with using strain gages for some time now on around 10 different factory chambered rifles is that when the gage is put on as directed and measurements are accurately taken from the brass and barrel O.D. that the factory ammo generated PSI is always without fail right near where you'd expect for the cartridge in question, I actually expected to see more variation or deviation in at least a couple barrels but simply have not.

I still have not fired any referance ammo in my dads 300 WSM to date for the simple reason it is always so close I don't really find it very usefull, if at all. We are going to try some factory stuff in it and the 243win next time out just for kicks and giggles. The main reason I see a need for a benchmark with factory stuff, or either handloads that you can set aside for later on, is if for some reason you suspect PSI readings are out of the norm at some time later on, you can go back and fire this ammo that was established to have a certain pressure, as your gage bond may have come loose or a connector on the wire may be causing added resistance outside the rezeroable range.

You have nothing to compair with except similiar calibers..

The confidence I have in developing loads in the two wildcats has only resulted from working with the strain gage systems and finding them accurate, if they were not, I would never have any confidence in them without factory ammo as a benchmark, period.

You can go with eratic velocity changes when working up loads like 39gr gives 3000fps and 40 gives 3300 fps or get to the point where you dont gain any velocity at all.. But what if you dont have any instances like this? How do you know what is to fast and how can you tell weather you have to much pressure?? Im gussin that sooner or later you will get eratic readings? Or you will get some other sign of pressure..


I would stay within average published maximum MV and charge weights, and work up to them too. At some point you will not even be able to reach either of those maximums before the load is too hot for your particular barrel, this is a fact of life tho... Erratic MV can be caused by many things, and pressure is related too, so if your MV jumps 300 fps with a 1gr increase on powder, which is highly unlikely but anything is possible, excess pressure would definitely have just indicated itself on extraction if you were nearing maximum pressure already, you'd know it just went way beyond now, by maybe even 10-15K PSI too.

Hot Core,

Turok and Dutch both make good points, why they even have to point these things out to you to begin with is my question? Anyone believing in CHE and PRE the way Hot Core does would jump on the opportunity to "personally" prove it works in a blind test

T/C,

If you forward the cases to me after you measure, I'll do the same CHE/PRE measurements too and forward the cases back to Denton, I'd forward them to Hot Core but it seems he wants absolutely nothing do do with this...

Of course I've "wasted" my "life savings" on this $189 PressureTrace module and this "worthless" laptop so I might have to get a bank loan to buy a blade mic for the test.

Simplistic and very inexpensive, well sometimes it takes a little bit more than that to attain accuracy at the level it needs to be for the desired result. If you don't desire that kind of accuracy, well that's one thing....

Sorry to wax statistical, but before we start, I want to get agreement on the test procedure.

As I understand it, PRE and CHE give you only an "OK/too much" reading. That's categorical data, which is the weakest type. If we want to accomplish our objective in fewer than 1,000 rounds, we have to get ratio or interval data (numerical indication of goodness). I believe the following procedure will do that.

Brent and T/C get to decide whether to use PRE or CHE. It doesn't matter to me, as long as they both do the same thing.

I will fully form 12 used 7.62x54R S&B cases, number them, and send them to T/C. He will measure them with a micrometer, and record his measurements. He will email his data to me. After I confirm that I have the data, he will destroy all copies, so his second readings cannot be influenced by his first. He will then send the cases on to Brent, who will do the same, and return the cases to me.

I will load them with various loads, and fire them at the range, and record the peak pressure, using my PressureTrace. Then I will send the cases around the loop again. This time, there is no need to destroy the data.

Now the stats part: I will subtract the initial readings from the final readings, and run regression on both T/C and Brent's data against mine, and choose whichever has the best R^2. This will be the data set that is most favorable for CHE/PRE being found acceptable. I'll run the best data set, with my measurement as the dependent variable, and T/C or Brent's as the independent variable. That way the residuals come out directly in PSI.

The residuals of this regression are the random error of the CHE/PRE method, confounded with the random error of the strain gauge system.

I'll use the uncorrected random error for the strain gauge system from my recent Varmint Hunter article, and subtract its variance from the total variance of the residuals, and take the square root of the remainder as an estimate of the random error of the CHE/PRE method.

The outcome of all that work is a standard deviation figure of merit for the CHE/PRE method. If this standard deviation is 2,500 PSI, for instance, it means that you can be 7,500 PSI (three standard deviations) above or below your target pressure, and not know it. If this number comes out less than 500 PSI, the PRE/CHE method is excellent. If it is less than 1,000 PSI, the method is good. If it is between 1,000 and 2,000 PSI, it is marginal, and if it is over 2,000 PSI it is dangerous.

The floor is now open for objections to the proposed procedure. Speak now, or forever hold your pee.

Denton, the only flaw I can see in a first, quick, reading, is that an "uninterested third party" should hold the measurement data of both parties. Ideally, the cases should be marked in such a way that the markings can be changed, in order to not let the first measurement influence the second. This could be done by marking the primer, and knocking it out before sending it back, but marking the case in another way.

Splitting hairs, I know, but this double blind stuff makes you do that.... HTH, Dutch.

Hot Core...

You are correct in stating that we are not going to use a box of factory ammo to establish a baseline.

That would be necessary if we were trying to establish a maximum load. That is not what we are trying to do. I have already established that. What we are trying to estimate is how consistently CHE/PRE can get the same answer, given the same input data. That's a different issue. Shooting factory ammo will not help answer that question.

Would you like me to send you a fired case, so you can instruct Brent and T/C exactly where to measure? Keeping my fingers out of the measurement technique keeps us all appropriately "blind".

Dutch....

Did I detect a volunteer to hold the data? In the end, I need four columns of data:

1) An identifier for each case. You can name them whatever you want, as long as you know which was originally which.

2) Brent's final measurement, minus Brent's intial measurement.

3) T/C's final measurement, minus T/C's initial measurement.

4) My pressure reading.

Each row of four is the data for one case.

Under these rules, everyone is on their honor to destroy all copies of their data as soon as Dutch confirms that he has them. I see only Dutch's final product, and nobody can look back to see what their answer "should have been".

denton - I'm still in, but now do not understand the logic behind what we are trying to prove, you lost me.

I was under the understanding that this was to find out if CHE/PRE (I have no idea what PRE is) measurements gave a safe idea to where maximunm pressure occured in a load. If this is still the case - I'll need (would like) 3 cases of known max pressure to develop a baseline.

quote:

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I'll use the uncorrected random error for the strain gauge system from my recent Varmint Hunter article, and subtract its variance from the total variance of the residuals, and take the square root of the remainder as an estimate of the random error of the CHE/PRE method.

---

I believe you have to take the total average variance minus one then that square root to find the deviation.

Help me out here - either I lost my spot, or something has changed. Either way I'll still measure for you. Brent will get the cases with my reference marks on them, hopefully that isn't a problem.

It helps to be dyslexic when you're doing statistics....

If we could make a batch of perfectly identical cartridges, measure them, fire them, measure them again, and take the standard deviation of the differences, an ideal measurement system would produce zero standard deviation. If we get a number larger than that, we attribute it to random error of the measurement system. This is a measure of the consistency of the system... its ability to get the same answer over and over, given the same input conditions. A measurement system that gets the same answer over and over again is "precise" or "repeatable".

There are problems with shooting identical cartridges. One is that I can't make perfectly identical cartridges. A second is that I can't interpret the results in terms of PSI. The process that I have outlined answers those problems.

Variances are sums of squares, divided by degrees of freedom. Standard deviations are square roots of variances. Usually, DF is n-1, which is where you are probably pulling up the n-1 thing. Variances simply add and subtract, but standard deviations do not, which is why you have to convert, add/subtract, and convert back.

So if we do all this, the end result tells us how far off we can be, before we can reliably detect it. With that, we can pick any baseline we like, such as a factory load, and estimate how much we miss the baseline before we know we have missed. Having done all that math, we can express that in PSI, not inches.

Ah! The penny drops!

I think you are thinking about the deviation rather than the variance.

The deviation is the difference between each data point and the mean.

Variance is the sum of the deviations, divided by degrees of freedom.

Standard deviation is the square root of the variance.

Your stats must not be in toooo bad shape if you're remembering all that ticky stuff.

Ooops... variance is the sum of the squared deviations, divided by degrees of freedom.

denton - Are we making this harder then it needs to be, or am I in a whole lotta trouble when my oldest starts coming to me with statistical homework?

Define for me "degree of freedom"

Whatever happened to you shooting your rounds, documenting your known pressures, sending the cases out to be measured by a second and third party, getting your cases back with our measurements and thoughts as to if your loads were over a given max pressure, then sharing the results and either displacing CHE/PRE or giving it some merit? I thought this was a test using real life people, guns, and their human error. The whole idea started around how erronious CHE is because of human error and to displace brass expansion at a given pressure. Figuring in variances and deviations isn't relevant.

Please don't read this as an excuse thread, I have nothing to loose in the outcome. I just want to keep it as fair for all interested parties as possible.

Like I said though, count me in, but keep all your readings handy - hopefully Brent and I can keep the cases straight (maybe numbered slots in the holder?)

6.5 Bandit,I found some problems in using a Chrony as a pressure guage.The rifle was an '69 unfired .264 FN with a 22" barrel.I made notes of the dia. ahead of the belt and the velocity.Max with a IMR 7828 3117f/s,with a 2" less barrel,mid 3000.Pop went the primer.This barrel had much more lands than grooves,so it was slow and spikey.It's getting rebarreled.

T/C...

Duh! After thinking about it for a minute, I decided the previous posts were about 10X too long and complex. Here's the short version:

The stated math will let you say that your "ruler" will let you get within 1/16" 95% of the time. You pick whether that's an inch, plus or minus 1/16", a foot plus or minus 1/16", or a yard plus or minus 1/16". You don't have to tell me in advance what distance you are going to apply this to. You can make that decision afterward.

Degrees of freedom:

Usually, the number of data, minus 1.

It is the number of independent equations you can write, without creating a conflict.

If you have four data slots, X1, X2, X3, and X4, and you specify the mean, you can set any three of the variables to any value you like, but the fourth is specified by the combination of the first three and the mean. So you have three degrees of freedom.

Denton,

I understand the reasoning for the number crunching, can't say as I understand the crunching part though.

I'm just as interested in the resolution of the measurement as I am identifying the point of max load, this will really determine how usefull it is in comparison to strain gage measurement systems.

Should be interesting, when do we start?

Brent - any ideas for keeping the cases in order? This may hinge off how denton ships them.

quote:

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Should be interesting, when do we start?

---

As soon as denton starts pulling the trigger.

[ 10-28-2003, 16:57: Message edited by: T/C nimrod ]

Wait, I didn't step forward..........Ohhhh, I see.....

Since I am the one keeping track of the numbers, I propose that we mark the primers. Color coded should be fine, unless the experimental design is looking for more individual loads than there are colors of Sharpies. Then we could number the necks, which can be removed using steel wool without affecting the micrometer measurements.

The primed cases will be loaded, and sent to be measured. When they are sent back, they will be numbered on the side of the case, shot, and run through a universal decapper (I have one laying around if you need one). That will remove the original designation, completely, before they are sent back to be re-measured. I will receive the measurements, both micrometer and strain gauge, and will compile them and publish them on this forum.

One request. When you shoot these, can you run them over a chrony? That way, we have another set of data at no expense, with both micrometer and strain gauge data to correlate with.

It would also behoove us to outline loading procedures, to make sure no-one argues about that aspect of things.

Finally, in my mis-spent youth, I did manage to accumulate enough college credits to qualify for a minor in statistics, so no funny business with the numbers.....! . Let's have-at! Dutch.

Denton - balls' in your court, let me know I'll PM my shipping address to you.

I like the idea of chronoing the loads as well - that may lead to another interesting finding.

Marking suggestion: I'll label the side of each case with a Sharpie. This can easily be completely removed with WD-40. It's then easy to relabel it with a Sharpie.

The cases will be formed, and ready to go today. I'll look for a PM from T/C, and probably get them in the mail to him today.

Sure, we can do chrono data along with the pressure data.

My intent is to load the cartridges with several different loads, all with respectable pressure levels, ranging from about 45,000 to 55,000 PSI. I'll load a few with 50, 51, and 52 grains of Varget, and 123 grain bullets, some with 50 grains of Varget and 150 grain bullets, and some a little north of 53 grains of H4350 with a 180 grain bullet. These are all loads that I commonly use.

Meanwhile, Brent and T/C, while the cases are in transit, you'll need to collectively decide whether to do PRE or CHE. Come to think of it, you don't both need to do the same process... I'm going to use the one that turns out most favorable to PRE/CHE anyway. Just be sure you tell Dutch what you did.

Last call for objections--

denton - you have PM

Brent - I'll do -whoops, can I say or no?- (that's the one I'm used to using)

Dutch - Would you prefer PM or email with the measurements?

[ 10-28-2003, 19:07: Message edited by: T/C nimrod ]

While searching the previous posts for a definition of PRE, I reread Hot Core's process for CHE measurements. Does it matter if my measurements are taken slightly different then the way it is described? I take three measuremnts around the case and average (as per Ken Waters process). Is this going to matter? Or just get a measurement to Dutch regardless of I get to it (for each case)?

Geez, another thread about how many angels can dance on the head of a pin.
Clark's method has stood me in good stead for a goodly number of years. Then I bought a Chrony. Now Clark's method and a Chrony tell me what I need to know about MY rifles. FYI for all you star wars types and gadgetheads, I've never blown up a rifle, nor removed a bolt from my nose, nor pulled splinters from my forearm, nor had to hammer open a bolt, nor had to remove a stuck case, nor..........etc etc. Have spent a lotsa time are the range shooting.

I think you can just do it your way. Be sure to identify to Dutch that you've used the Ken Waters method.

If Brent wants to do it the other way, taking the largest diameter, then I can test both methods.

T/C,
I'll email you my address.

Dutch,
I'll need yours I guess.

I really don't care how the cases are marked, just as long as we can tell them apart. Actually you could mix them up and mark them with a code that Denton could give Dutch to go back and match them up, the code would be different each time around. "A" might = case #7 and "D" case #2 in round 1 for example.

That way no fancy stuff could be done no matter if one wanted to or not, and also measurements for each code could be forwarded to Dutch. Both of us could also save our measurements to see if the code was deciphered properly, assuming the code was changed on the second round and the code was posted at the same time the results are.

I really wish WD-40 or any liquid not be used inside of the case during the test, and the code be wrote on the outside of the neck, on two sides just to be safe.

If we measure PRE and CHE both, we'd get the scoop from each, which is what I'd like to do.
The distance up the case is important on PRE measurements so any suggestions where exactly you'd like them to be taken at?

Cases are on their way to T/C.

They are unprimed, since I didn't want to send primed brass through the mail. You'll find slight neck dents, which are no problem, since this old cartridge headspaces on the rim. I usually only neck size, since the chambers on my guns seem to be just a trifle long.

I bumped the sample up to 15. If something goes wrong with one or two cartridges, we'll still have enough, and we might be lucky and get all 15.

I used white plastic tape to mark each of them. I think the right procedure is for each of you to send your data to Dutch, and for Brent to return the cases to me. I'll re-label them with a Sharpie pen, directly on the case, with a new ID, prime, load and fire them, and start them back around the circuit.

When Dutch sends me the data, he can strip both the old and new ID off the data files. The ID is just there to help keep the bookkeeping straight. All I need is a PRE, CHE, and corresponding pressure number for each case. We'll each be sending that to Dutch, and he will assemble it.

T/C, is your method considered PRE or CHE? Whichever you do, Brent should do the other.

Denton,

I believe Hot Core recommends the cases need be FL, or P-FL resized between PRE measurements? I planned on taking measurements of PRE and CHE both and forwarding this to Dutch, you don't want to compare our readings of both? Forgive me if I'm a little lost on the how's and why's at this point. You just let me know what you want me to measure, if I don't follow you now maybe I will when we're done.

it would be great to see these results...

Myself, I use published data and quickload for a starting point (once I got it), a chronograph to verify, CHE, and I look at the primers... I've only been reloading most of my life, so feel free to call me inexperienced. I've also found that, for modern powders/brass/new carts, the manf will talk to you about other powders listed.

I will state my STRONG opinion that anyone without a chronograph should NOT persue some "top load" in terms of suspected velocity, as they have no way of meassuring their results accuratly.

Am I the ONLY person that's fired factory ammo, even in a factory gun, and been surprised that the appearence of the primer and the lower than expected velocities?

And, just asking, how many of you have found your velocities LOWER and/or HIGHER than expected?

jeffe

For me, email works fine. If you fellows would drop me a line so we get get this triangle set up; use the address listed here.

Once I get the measurements, I will tabulate, identify the methodology of the measurements, and publish here (on a new thread). For grins and giggles, I'll take the first crack at the ANOVA, but I will have to get some books out of the bookcase, first....

Now, when we get this published, I propose we spend the proceeds on pizza and beer for the party..... Dutch.

I'd be delighted to have both PRE and CHE data from both of you.

If I understand the method correctly, for CHE, you measure the diameter of the case head, just forward of the extractor groove, after FL sizing, and again after firing. The difference between these two readings is the Case Head Expansion. I lifted this from the Barnes site:

quote:

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If you have case head expansion of more than .0005" with a once-fired case, this is a sure sign of excessive pressure. You will have to measure your case head with a Blade Micrometer just in front of the extractor groove, or you can use a regular micrometer and measure the belt on belted cases, before and after shooting. When any of these signs appear, back down one full grain and you will have a max load for your gun.

---

If I read Hot Core's instructions correctly, for PRE, you get a little pressure ring on a fired casing, just forward of the case head. This is visible, even after the case has been FL sized. Again, the number that counts is the difference between the just-formed dimension, and the just-fired dimension. I think this requires a blade micromenter as well, because the taper of the casing would "fool" regular anvils.

If anybody has information contrary to this, please jump in. I'm no expert on this method.

The casing being circulated have been fired 2-4 times, so they are within Hot Core's limits. They have been full length sized, marked, and trimmed.

This quote caught my eye, though I didn't read all of the previous posts. If I am repeating, I apologise....

"If I understand the method correctly, for CHE, you measure the diameter of the case head, just forward of the extractor groove, after FL sizing, and again after firing. The difference between these two readings is the Case Head Expansion."

The way that I understand this process, is that you have to have a "standard" to compare your loads to. Factory loaded ammunition is that standard.

To compare your reloads to factory ammunition, measure the average case head diameter (ahead of the groove) on some factory cartridges, record for each cartridge. Pull the bullets/powder from an equal number of factory cartridges (same lot of brass!), and measure & record casehead diameter for these brass cases. Load these cases with your load. Shoot both the factory loads and your loads. Measure all of the casehead diameters after firing, and figure the differences for each case. If the difference/"growth" is larger for your reloads than the factory loads, pressure is higher, if less, pressure is lower than the factory loads.

You can't just measure before/after firing just your reloads on new/once-fired brass - because you are not comparing them to a known standard. This process makes sense to me, and seems to remove as many variables as possible.

Regards, Bill

Bill M...

That's a really good suggestion. Thank you.

denton,

I can't take "credit" for it, as I didn't think of it, and am just recalling what I remember about the process, but you're welcome just the same! The differences are going to be minute, so you have to be able to measure to "tenths" (.0001") to get valid comparisons. The larger the sample size the better.

Good shooting!,

Bill

Bill,

I understand where you're coming from, as cases will, and do vary in capacity.

I believe the method Hot Core promotes and says is accurate, is simply keeping the expansion to .0005" or less from the brass measurements taken from brass in its fire formed state. Sizing it back down will change the PRE measurement but not the CHE measurement accross the case head. The point is to look for expansion over and above the initial fire formed measurements in the amount of .0005" and that is where to stop.

It is probably better to start with factory ammo for the initial expansion, but I believe as long as the load is not in excess of 60K PSI or so, the case will expand about the same each time and not increase past the initial expansion diameter.

I measure across the belt, or across the case head on the forward edge above the extractor groove... not with a blade mic, but rather an outside mic like T/C.

PRE is a bit different and should be measured at the "largest" diameter above the case head, it's not hard to find, as it's at the first visible contact point with the chamber wall above the casehead, below this the case head keeps it from expanding to contact the chamber. There's sometimes a problem though, and that is if the chamber is cut tight the pressure ring is not always the widest point above the casehead, sometimes the case head itself still is.

The other problem, is that if the opposite is true, and the chamber has plenty of clearance at the base and the pressure ring is pronounced (Larger dia than is the CH), the outside mic will work for PRE but NOT for CHE. PR has a "peak, or ridge" that the outside mic will measure but there will be an angle from the CH up to the larger PR diameter so the outside mic will no longer work without a flat or peak to measure from, it just won't be accurate without a blade. This is with a non-belted case that is.

I'm not spending $150 for a blade mic for this test, so unless I find one cheap around here I won't be taking measurements where it won't be accurate without one. What ever I can get with this outside mic will have to do, but I'll check some pawn shops around here for a blade mic just in case they have one cheap.

Bill,

"If I understand the method correctly, for CHE, you measure the diameter of the case head, just forward of the extractor groove, after FL sizing, and again after firing. The difference between these two readings is the Case Head Expansion."


My understanding is the case head cannot be sized back down, only the pressure ring can. The measurement immediately ahead of the extractor groove across the case head will remain the same diameter after the initial forming to your chamber, unless you exceed the maximum suggested pressure for the case, this is the way I understand it. If you get as little as .0005" expansion beyond this point you've exceeded this pressure, so they say that is.

Once the brass has been subjected to repeated overloads and the case head diameter has increased to the point it will no longer chamber it's toast, as the die will not size the base of the case that low, that or the belt or just immediately ahead of the belt a few thou.