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Here is some actual data from a Finnish Mosin instrumented with a strain gauge. The standard deviation of the random error in that particular system has been measured at 335 PSI, which is practically the same as a good piezoelectric system. The case head measurements were made with a Mitotoyu blade micrometer, clamped to a granite inspection block to ensure that all measurements were made at the same height on the case head. Since cartridge cases are not perfectly round, three measurements were made on each case at different orientations, and the three measurements were averaged.

The brass was all from the same batch, having been fired once.

Note that there are two rounds that were over 60 KPSI that measured .0001" or less of case head expansion. If you follow the 95% PI intervals across the chart, .0003" represents something between 49 KPSI and 75 KPSI. Close enough for you?

The R-Sq value shows that 23.5% of the change in case head expansion is attributable to pressure, and the remaining 76.5% is attributable to random error. If you like a measurement system that is 3/4 random error, then CHE is for you.

No matter what you do, case head expansion is NOT a reliable pressure indicator. If it were, that's what industry would use.

You will not look better with a rifle bolt where your nose once was.

Last edited by denton; 04/27/17.

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Originally Posted by denton
As a very rough rule of thumb, pressure signs start around 70 KPSI and primers fall out around 80 KPSI.


Depends on the primer too.

Winchester will show signs before CCI.


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Originally Posted by antelope_sniper
Originally Posted by denton
As a very rough rule of thumb, pressure signs start around 70 KPSI and primers fall out around 80 KPSI.


Depends on the primer too.

Winchester will show signs before CCI.
and seems some win. primers will leak aT Mexican food fart pressure

Last edited by ldholton; 04/27/17.
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Originally Posted by ldholton
Originally Posted by antelope_sniper
Originally Posted by denton
As a very rough rule of thumb, pressure signs start around 70 KPSI and primers fall out around 80 KPSI.


Depends on the primer too.

Winchester will show signs before CCI.
and seems some win. primers will leak aT Mexican food fart pressure


I've seen those reach 80,000 psi pretty easily.



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Best pressure sign I know of is having to beat the bolt open with a rubber mallet.


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Originally Posted by MissouriEd
Best pressure sign I know of is having to beat the bolt open with a rubber mallet.


That, and the self-depriming case . . .

It still amazes me that there are folks who think CHE is a valid method.


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I don't know anyone that has actually conducted Piezo pressure testing and considers "Traditional Reloader Signs" as valid pressure indicators for load development.

Piezo is certainly not perfect...but it is better than most anything else we have.

Strain Gage is a pretty good method of measurement. Same comment applies.

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Beyond published velocities would be a fair indicator as well.


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Originally Posted by denton
[Linked Image]

Here is some actual data from a Finnish Mosin instrumented with a strain gauge. The standard deviation of the random error in that particular system has been measured at 335 PSI, which is practically the same as a good piezoelectric system. The case head measurements were made with a Mitotoyu blade micrometer, clamped to a granite inspection block to ensure that all measurements were made at the same height on the case head. Since cartridge cases are not perfectly round, three measurements were made on each case at different orientations, and the three measurements were averaged.

The brass was all from the same batch, having been fired once.

Note that there are two rounds that were over 60 KPSI that measured .0001" or less of case head expansion. If you follow the 95% PI intervals across the chart, .0003" represents something between 49 KPSI and 75 KPSI. Close enough for you?

The R-Sq value shows that 23.5% of the change in case head expansion is attributable to pressure, and the remaining 76.5% is attributable to random error. If you like a measurement system that is 3/4 random error, then CHE is for you.

No matter what you do, case head expansion is NOT a reliable pressure indicator. If it were, that's what industry would use.

You will not look better with a rifle bolt where your nose once was.


So out of curiosity, did anyone section the cases, and run some microhardness measurements on the brass, to determine the hardness range in the case webs? It would also be worthwhile to measure the internal dimensions of the brass, to see if is consistent. You mention it's a Mosin, so 7.62x54R. I never have worked with one, but I would wonder how consistent the brass is made for them - quality or plinking grade.

Measurement error is a fickle witch, and I've run into it many times over the years in manufacturing. The one I always remember is some stampings that we heat treated, which had to be tested at a GM-approved lab for hardness, to be approved as first articles. The lab significantly disagreed with our testing. After a week of head scratching and phone calls, I sent the same specimen to a different GM approved lab. They agreed perfectly with us. So I submitted the first articles with their test report smile

I agree, you can't say .0002" expansion is 50ksi, .0004" is 60ksi, etc. Too many variables are in play. But I'm still going to measure case heads, because if they're expanding too much, there's a problem, regardless of what the chrono or other instrument is telling you.


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What is "too much" expansion?


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In a strong modern action, bolt or falling block single shot, more than .0005" would be a red flag to me. Especially if the chrono likewise shows higher velocity than expected.

In older guns, or weaker style actions, follow the book & the chrono.


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Book velocity or max charge, whichever comes first, at least for me.


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tex n cal,

And how did you arrive at .0005" as the magic number?


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Chronograph and common sense are my guidelines.

Too good is too good. Puzzling is puzzling.

I've blown up a few. The chrono doesn't lie.



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Originally Posted by Mule Deer
tex n cal,

And how did you arrive at .0005" as the magic number?


It suggests to me that primer pockets are going to be loose in 2-3 firings, which is too soon.


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The diameter of a primer pocket grows about 2X as fast as the OD of the case head.


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<shrug> it's a "red flag" for me - meaning stop & evaluate what's going on. Bear in mind in the past 5 years I've seen 3 instances where reasonable loads produced excessive case expansion, without any other indicators of high pressure, so that's one reason I'll stick to CHE.

I look at a variety of factors to judge what to do with a load - speed, accuracy, case life. If all three are good, and the bullet is appropriate for the task at hand the load is a keeper. smile


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The thing is with case head expansion (and I do use it from time to time), it will not tell you what your pressure is but if there is measurable expansion, you can be fairly certain it is too hot. I must also mention; a lack of expansion does not necessarily mean a load is safe. Rocky Gibbs was a believer that the brass was the weak link and looked for the hardest brass he could find so he could load hotter. His feeling was, if case life is good, the load is safe. Unfortunately, a lot of his customers skipped over the brass recommendations and blew the primers right out of their commercial Remington brass.
Speer used case head expansion in developing some loads in their early manuals and some of those loads are HOT.
If a rifle chamber is cut so that it allows no expansion, it will obviously have an effect, This is especially true with rimmed cartridges where most of the cartridge is contained in the chamber. GD

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Originally Posted by greydog
The thing is with case head expansion (and I do use it from time to time), it will not tell you what your pressure is but if there is measurable expansion, you can be fairly certain it is too hot. I must also mention; a lack of expansion does not necessarily mean a load is safe. Rocky Gibbs was a believer that the brass was the weak link and looked for the hardest brass he could find so he could load hotter. His feeling was, if case life is good, the load is safe. Unfortunately, a lot of his customers skipped over the brass recommendations and blew the primers right out of their commercial Remington brass.
Speer used case head expansion in developing some loads in their early manuals and some of those loads are HOT.
If a rifle chamber is cut so that it allows no expansion, it will obviously have an effect, This is especially true with rimmed cartridges where most of the cartridge is contained in the chamber. GD



Yea,

I used to shoot some load out of an old Speer manual......until I figured out they were waaaaayyyyyy too hot.....


You didn't use logic or reason to get into this opinion, I cannot use logic or reason to get you out of it.

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Originally Posted by denton
The diameter of a primer pocket grows about 2X as fast as the OD of the case head.


Different brands in various cartridges may react differently. For example, Remington nickel-plated brass used in a Ruger No.1 in .45-70 would handle 60,000 to 63,000 psi (as measured by a US lab) for at least 10 firings with no discernible primer pocket expansion (using WLRM primers). They were then thrown out. Federal nickel-plated .45-70 brass couldn't begin to handle that psi before primer pockets were loose enough to not hold new primers.

The report from the head ballistician to me was, "You have just reinvented the .458 Winchester Magnum, what was the recoil like?" From a 24" test barrel their average MV was 2096 fps from the 500gr Hornady Int. RN. A rep from Ruger told me, "The Ruger No.1 in .45-70 is just as strong as a Ruger No.1 in .458 Winchester Magnum.

The word from that well known ballistician was "That load is safe in your Ruger No.1". No one in that lab had any previous idea that using the right powder, primer, case and bullet, that a .45-70 case could safely be used at those specs in a rifle capable of easily digesting it. I was getting an average of 2015 fps. My "new" Ruger in .45-70 had the throat lengthened nearly twenty years ago for even better performance by seating bullets "long".

There are opinions, and then there are facts.

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