Since this has become a BIG topic of late, I thought I would post the actual pressures required to YIELD (meaning a lasting deformation one CAN measure after firing of the case) most modern case heads across a brass hardness range which is realistic.



This chart provides the maximum allowable chamber pressures for 1/2 hard cartridge brass, which specifies a minimum yield strength of 42,000 psi. This is SOFT stuff, like dog turds.









This chart provides the maximum allowable chamber pressures for 3/4 hard cartridge brass, which specifies a minimum yield strength of 55,000 psi.







Finally, this chart provides the maximum allowable chamber pressures for full hard cartridge brass, which specifies a minimum yield strength of 65,000 psi.









Anyway, if YOU ARE MEASURING A PERMANENT PLASTIC DEFORMATION OF A CARTRIDGE CASE HEAD,YOUR CHAMBER PRESSURES ARE AT LEAST THIS HIGH, OR YOU BRASS IS THIS SOFT!!!!! This is fact not fiction.

CASE HEADS SHOULD NOT BE YIELDING ( you should measure NO difference in case head (diameter of the extraction groove) before and after firing) < !--color--> IF YOU ARE RELOADING TO SAAMI OR CIP SPECS!



You will also notice that some cartridges will yield their webs LONG before showing any signs of pressure at the primer! So be advised, the extractors on most rifles have a considerable amount of clearance to the extractor groove. This means that it can take many shots before you will see an extractor mark on your cases. So those suddenly hot loads you shot last week, you know the ones that you shot 3 times before without any pressure signs, that are now suddenly showing pressure signs from extractor marks. Guess what, the pressure has more than likely ALWAYS been higher than heck, it just took three or four firings to bend the case's web into the rifle's extractor!



ASS_CLOWN

Here are pictures of many sectioned rifle cases, the sections provide a cross-sectional view of the case head and forward into the "pressure ring" portion of the case. It is important to understand that the ONLY portion of a cartridge case which IS NOT supported by the barrel IS the CASE HEAD!







From left to right:

223Rem, 9.3X74R, 30-06, 308/411, 458 Win mag, 416 Rigby, 500 Jeffery, and 50 Beowulf.



The case head thickness of all cartridges are practically identical ranging from ~ 0.195" to 0.210". The following pictures show the case head dimension of each sectioned case.



223 Remington (milsurp case) The case head is 0.191" thick.







50 Beowulf (Starline brass) This is THIN stuff! The web is only 0.085" and is the primary failure mode of this brass at pressures around 45000 psi. The case head is 0.182" thick.







416 Rigby (Norma case web is ~ 0.115") The case head is 0.210" thick.







308/411 (Remington 308 Win case web is ~ 0.112") The case head is 0.205" thick.







500 Jeffery (Bertram case web is over 0.125" thick) The case head is 0.196" thick.







458 Winchester Magnum (Winchester case web is ~0.115" thick) The case head is 0.195" thick.







30-06 (Winchester case web is ~0.112" thick) The case head is 0.208" thick.







9.3X74R (Norma case) The case head is 0.207" thick.







The 9.3X74R case is about to suffer a head seperation. This is good, in that it illustrates the exact location of the "Pressure Ring Expansion" region of the case. Head seperation occur where the brass stretches the most, in other words, where the most Expansion occurs.







You will notice that the thinning of the brass (head seperation) occurs at the forward termination of the radius which blends the bulkhead that is the case head to the case walls. In belted magnums the "Pressure Ring Expansion" area is immediately forward of the belt. This is due to a large section differential at this point (look at the 458 Win mag section for clarification).



There is NO doubt that the "Pressure Expansion Ring" does increase in diameter after firing. It also is without doubt that this ring does provide some insight into barrel deflection during firing; therefore, providing some insight into operating pressure (although it is a VERY MURKY insight).



The case head, which is the disc of brass at the base of the cartridge with only the primer pocket and flash hole piercing it, SHOULD NEVER PERMANENTLY DEFORM DUE TO FIRING OF ANY LOADS! If your reloads are causing a permanent deformation of the case head (this deformation will be at a MAXIMUM in the extraction groove of a rimless case) you should back you loads off at least 10%!!



By the way, the case head of the 9.3X74R is STRONGER that either 416 Rigby or the 500 Jeffery (which share a common extraction groove diameter, or close enough it doesn't matter).



Rimmed cartridges have immensely STRONG case heads, as such they DO NOT exhibit "normal" pressure signs like leaking primers, and case head expansion, until it is often TOO LATE! Too late meaning the rifle has blown up!



ASS_CLOWN

Hey AC, Nice flicks. Looks like you have put a lot of work into getting them.

Quote:

---

Rimmed cartridges have immensely STRONG case heads, as such they DO NOT exhibit "normal" pressure signs like leaking primers, and case head expansion, until it is often TOO LATE!

---

Absolutely an excellent point. Here isa situation where I've always recommended that folks "avoid" CHE because the SAAMI Pressure is too low to show CHE in most Rimmed Cases like 30-30, etc., and they should use PRE which workswith ALL Cases. But, your explaination is also quite relevant and shows effectively why it is best no to overload them.

For those of you who are wondering where PRE is measured, look at his last picture. You measure PRE on this non-belted Case where the Insipient Casehead Separation is located.

If you Partial-Full Length Resize bottle necked cases, you create "Zero Headspace" which helps prevent this separation from occurring. And as a major side benefit, P-FLR also forces the bullet to align better in the chamber resulting in better accuracy.

You are also more likely to have a case head separation on a belted or rimmed case, because it doesn't headspace on the shoulder unless the die is properly adjusted to do so. The PRE is always a bit shaky, especially in factory-chambered rifles, as the individual chamber can be slightly out of round, etc. and some will show PRE with any load if measured in this area. Most of the custom barrels have more time to spend on chambering and will be set up tighter and with minimum headspace.

Just one small addendum to AC's post:



If the case head is expanding, the primger pocket is expanding too, but at a faster rate.



If you cross section a case, or just look at the base, you have two circles, the OD and the ID, where the ID is the primer pocket or the flash hole, depending on where you section.



If you think about where and how the brass can flow, you'll see that the area BETWEEN these two circles (area of the outer circle, minus area of the inner circle) has to remain constant.



The fairly surprising result is that the ID of the primer pocket expands faster than the OD of the case head, by quite a bit. In the case where I worked through the math, the primer pocket grows 2.3X as fast as the OD, but that will be different for different geometries.



So, if you run a kajillion PSI, and stretch the OD of that cartridge .001", the primer pocket will expand .0023". Since primers have a .0005" to .0025" press fit, practically none of the new primers you put in that case will "stick".



Anyway, the teaching of AC's post is extremely important: The pressure at which you start to see yield depends on case geometry. If you happen to have half hard brass, yield, and case head growth, starts somewhere between 37,000 PSI and 80,000 PSI, depending on which cartridge you're measuring. The figures for 3/4 hard and full hard are different. I know of no convenient way to determine how hard the brass is, so I don't know which table to apply to any batch of brass.



One sorta nit: Ackley hotly disputed the notion that rimmed cases are stronger than more modern ones.

Denton,



Thanks for that addendum. Ackley said a lot of things I often question. Look at that 45-70 blown to pieces up on the "African Big Game" forum. The case was supposedly intact, if I read correctly, the gun however is blown literally to pieces. The barrel blew in classic over pressure loading. The thing could be used for a case study in a textbook, for crying out load. I have only seen RIMMED cartridges wreak such destructive havoc. The rimless always seem to blow the primer (aka yield the case head) and vent the excess pressure back through the action, which can be VERY bad if there is not an adequate gas management system back there (you know your eyes are only inches from the breech).



The rimmed case, that is the one with incipient case head seperation, is a 9.3X74R. It is from a SXS double rifle, which are notorious for seperate case heads.



ASS_CLOWN

Well, of course, Ackley's opinions are as subject to question as the rest of us. I'll have to look and see if he did any experiments to find out... that's one thing I really like about him. If a question came up, he'd go try something to test it.



At first, I thought I was perfectly clear on the charts you posted. Having looked at them closer, I'm not sure I'm understanding.



The ID of the web is smaller at the flash hole than it is at the primer pocket. So at the flash hole you've got more brass to constrain the pressure, and it seems to me that it would take more force to expand the brass there than at the primer pocket. The reverse seems to be shown in the tables. Can you give us a little more on what exactly is being measured here?



One thing about the old rimmed cartridges is that a case split is usually no big deal. I was shooting surplus ammo in a Mosin, and discovered after the fact that I had several split cases, up near the shoulder. The bad news is that the Mosins apparently don't manage ruptured primers very well. I guess that is good reason to load them gently.

Denton,



The charts illustrate the chamber pressure required to:



1.) Yield the web of the case due to internal case pressure acting against the web of the case i.e. closing off the extractor groove. This is an entirely different calculation to the other two.



2.) Yield the case through the flash hole / case head OD section



3.) Yield a through the primer pocket / extractor groove seciton.



Cleaer as mud? If I still had some failed Beowulf cases it would be very easy to section one and show what I am talking about. This is the primary failure mode of the Beowulf, web yielding that is, and it pinches the extractor groove shut so to speak.



ASS_CLOWN

Aha! The penny drops. Thank you.

That's very useful information. What's the source?

I have gone through the exercise of trying to figure out the difference of pressure required for the primer to fall out of 7.62x39mm brass in two cases:

a) small primer, like RP brass

b) large primer, like Winchester brass



If I rms add the hoop stress around the primer pocket with the axial pressure on the brass caused by the case sliding back into the breech face, I find that the hoop stress becomes insignificant.



That is if the hoop stress in tension is 10% of the axial compression stress, after rms, the hoop stress is only .5% contribution.

Clark,



I am not sure I follow you, rms??? RMS (root mean square) is an averaging methodology and as such is not typically used for stress applications. The conventional methodology for examination of the effects of combined stresses is "von Mises".



By the way, if I follow you correctly your analysis doesn't match up with actual test results. I know primers are blown and case heads expand at high pressure, I believe you have posted this on several occasions yourself, however, if your rms method is correct then compressive stress is dominant. Compressive stresses acting upon the case head will have the effect of peening the primer pocket shut, thus reinforcing the primer and NOT allowing it to blow out.



A logic problem alone will answer your question as to which 7.62X39 case (large primer versus small primer) will handle the most pressure. The small primer will it has more material to support the loads.



Logically it is like asking, which will handle more load, a 2X4 or a 6X6 beam. The answer is rather obvious.



If I misunderstood your method/point please enlighten me.



By the way, the initiation of a primer pocket failure does not occur at the mouth (opening of the primer pocket), but in the section through the primer pocket bore and extractor groove.



ASS_CLOWN

AC,
I knew I was in trouble with that post when I woke up this morning. I said to my wife, "I've gotta check that rms'ing .1 and 1 will give 1.005."
She said, "It's called ""rss'ing"" and left.
Now you point out:
1) I should be Von mises'ing
2) Pockets are not crushing to a smaller diameter.

Could you work an example of Von mises'ing the hoop stress and the axial compression in the brass around the primer pocket?

Clark,



I have a headache this morning, of course you did not know that, von Mises stresses acting in the case head. Yes, my head is throbbing NOW. How shall we model the thrust force? In reality the thrust force acting against the bolt face (thus the case head) is NOT equal to the internal pressure X the internal area of the case. The thrust force acting against the bolt face (thus the case head) is reduced by the axial spring rate of the walls of the case head. This is a slightly non-linear problem as the case does stretch plastically, which complicates the computations just a tad.



I will see what I can put together. I will try and make it realistic, and will post the results for a few different case heads.



So in the end what I am saying is give me a couple of days. I need to take measurements off of different case heads, build the models, and crunch the numbers.



Denton,

With regard to source materials. These are calculated stresses, but several have been correlated to actual case failures in rifles of correct dimensional condition (meaning the chambers and head space were well within spec). For instance the 50 Beowulf WILL yield a case web at ~ 45 psi +/- ( due to geometric and mechanic propertie variations case to case). The 308 Winchester will blow a primer and yield the case ~ 77ksi +/- (due to geometric and mechanic propertie variations case to case).



Regarding source material, I am fond of Dr. Shigley's "Machine Design" textbook (actually he has several, I find the thicker the better) for a handy reference. Practically any well written text book on "Strength of Materials" or "Machine Design" should provide with the appropriate concepts of Physics to derive the necessary equations to solve the vast majority of these problems to a reasonable level of accuracy.



ASS_CLOWN

RSS = Root Sum Squares... the way you add up things that add by squaring, and taking the square root of the sum. But you probably knew that.

AC, the tables themselves show something that is true, that has been missed in a lot of the literature: Setting a single growth criterion for all cases ignores basic physics. The pressure that will cause .0005" growth in a 223 Rem is entirely different from what will cause the same growth in a 416 Rigby, even given identical properties of brass. If the charts are out of a book or article, or if you just did the calculations, it would be cool to know the source.

Denton,

I did the calculations in those charts. They are based on a two dimensional analysis. Clark has asked that I perform a von Mises calculation in three dimensions, at least that is what I understood his desire to be.

So we will look one or two case heads, and the stresses at the primer pocket and at the extractor groove diameters. We will consider the radial, tangential (hoop), and longitudinal forces acting upon the case head. I was not able to find anyone with some spare time to model the case head so I will have to do it the long and hard way, by hand.

I will try and get Clark's analysis done this weekend, we shall see.

ASS_CLOWN

AC,
Thanks for the response, I hope I don't slow this excellent thread down with my comments, but:
1) previous thread on this
I assumed that the pressure inside the case body times the area created by the largest cross section in the body, was the axial thrust that would push the case head into the breech. As you said, that force must first have the case wall axial tension subtracted. I could wave my hands and say, "smooth chamber and moly bore paste on the case", but there would still be friction.
2) The shape of the primer pocket is shallow, and my modeling it as a cylinder with hoop stress is an over simplification.
3) I found SKSs can be poor test platforms, unlike 98 Mausers, but replacement parts have arrived.
4) I have thought of cutting extractor grooves deeper to get another data point to solve for the friction.
5) There is the annealing, you suggest, of test brass to a softer state, could give more data when tested to extractor groove expansion.
6) There is making brass without extractor grooves for test.
picture of 10mm brass made from 30-30 brass, overloaded

This has turned into a really interesting thread.

AC, I'd suggest you write up some of this stuff. I can put you in touch with at least one editor that would probably pick it up.

You tables were kind of a jaw-dropper for me. I had realized that the radial pressure of gasses in the pocket and flash hole would exert outward pressure, and that different thicknesses of brass would go into yield at different pressures. That clearly means that if you could get a good expansion rule for one caliber, it would be useless for other cases, with different dimensions. But getting some numbers on it was a real surprise.

BTW, Ackley experimentally found that primers drop out at about 80,000 PSI. That's probably in something with an '06 base.

Clark,

Barring any mistakes, that I did not catch going through the computations three times (I am pretty darned sure it ain't screwed up) here are the numbers, per you request concerning combined compressive and hoop stresses via von Mises theory on the subject (which currently is the accepted norm). I did include a reduction in bolt thrust force due to the spring rate of the cartridge case (this was assumed linear for this first run, although in reality it almost certainly contains a non-linear portion).

Analyzing a Mauser bolt head (.470" base diameter rimless case)

Chamber pressure - 77,198 psi

Case spring rate at the case head/body junction - 6,271,097 lb/in (see assumptions below on calculation of spring rate)

Simple Compressive stress acting on case - 79,487 psi

Hoop stress (simple tensile stress) at outer diameter (extractor groove OD) - 65,000 psi

Hoop stress (simple tensile stress) at inner diameter (primer pocket dia) - 142,198 psi

von Mises stress at outer diameter (extractor groove OD) - 73,324 psi

von Mises stress at inner diameter (primer pocket dia) - 123,432 psi

Notes:

As I stated earlier the case head yields (fails) from the primer pocket diameter outward to the extractor groove. Tensile forces are a maximum in the primer pocket and a minimum at the extractor groove OD (they are still over tensile yield though).

What the analysis is saying is. The compressive thrust load is causing the primer to compress (DUH). This compression of the case head reduces the net strain energy in the primer pocket, but increases the net strain energy in the extractor groove. Hence the von Mises stress is lower in the inner diameter (primer pocket) than the simple stress calculation predicted, but the von Mises stress is higher at the outer diameter (extractor groove) than the simple stress predicted.

Some things to understand. von Mises stresses by their very nature comprehend that in reality complex stress conditions to not conform to the stress limits of simple axial, bending, shear, and compressive stress models. What this means is that the von Mises stress, although higher than the simple tensile hoop stress calculation, do not mean that the material in question is any stronger. In other words, while book values for tensile strength are adequate to establish "limits" for simple tensile stress calculations, these same tensile limits to not correlate well to von Mises tensile stress calculations. That is most likely as clear as MUD! Sorry but I cannot think of a better way to explain it off-hand.

von Mises stress calculations are an evolution of the distortion / energy theory, a theory I still think holds some merit, at least as a concept to understand strain plot diagrams. Anyway, these two methods of combining triaxial stresses are related, and if you can understand one you can most likely understand the other. I am not sure what is available free on the web, but if you get a copy of one of Dr. Shigley's Machine Design textbooks he does provide a reasonably good explanation on the topic.

The case spring rate was estimated using mechanical properties of 70-30 brass and assumptions as follow:

Young's modulus - 16,000,000 psi

Expansion length (length of brass stretching) - 0.13" This is based upon two times the measured length of the thinning of a case wall just prior to case head seperation. The average width of the thinned section is 0.065". I simply double it.

Length case had to travel in chamber to contact bolt face - 0.010". I assumed standard chamber and case tolerances. This was not a "necked sized" and match chamber analysis.
grin:

I hope all this makes some sense. I do not like to get so technical on the web as it seems to scare people off. This is not trivial stuff, and is in many ways pretty damned deep. I find this stuff somewhat difficult to put into layman's terms, so I apologize if I did a poor job.

ASS_CLOWN

Here is a work up in .308 [Mauser case head per chart at top of thread] that should yield at 77 kpsi if the Win brass is full hard.
Quickload thinks that the extractor groove started expanding at 78kpsi.

Hodgdon max book load:
308 WINCHESTER, CASE: WINCHESTER, BBL: 24", PR: FEDERAL 210M, 168 GR. SIE HPBT COL: 2.800" H335, 42.0 gr., 2631 fps, 49,300 CUP

My test:
Pacific .308 Win reamer, VZ24 trued action, A&B fluted stainless 24" F54 barrel, H335, CCI200 primer, 2.9" OAL, Speer 168 gr. HPBT Gold Match, brass: Win308Win:

0) 42 gr. QL= 2565 fps & 46 kpsi, 0% overload, did not load 42 gr.
1) 43 gr. QL= 2618 fps & 49 kpsi, 2% overload, ok
2) 44 gr. QL= 2670 fps & 52 kpsi, 5% overload, cratered primer this and higher
3) 45 gr. QL= 2722 fps & 56 kpsi, 7% overload
4) 46 gr. QL= 2774 fps & 60 kpsi, 10% overload
5) 47 gr. QL= 2825 fps & 64 kpsi, 12% overload
6) 48 gr. QL= 2875 fps & 68 kpsi, 14% overload, mark on brass from bolt face extractor this and higher,
7) 49 gr. QL= 2925 fps & 73 kpsi, 17% overload
8) 50 gr. QL= 2974 fps & 78 kpsi, 19% overload, extractor cut on brass expands .0020"
9) 51 gr. QL= 3024 fps & 84 kpsi, 21% overload, extractor cut on brass expands .0020"
10) 52 gr. QL= 3073 fps & 90 kpsi, 24% overload, extractor cut on brass expands .0110", primer fell out,

Picture of the 10 pieces of brass fired

Clark,



Considering the geometric difference case to case (aka tolerances) and the fact that I am using MINIMUM material specification tensile strength data, I think the analysis is descently close to reality.



Will wonders never cease.



By the way, thanks for sharing that REALITY data point!! I must admit that is has been awhile since I decapped a 308 the "easy" way.



ASS_CLOWN

Hey AC, No wonder CHE and PRE work so well with all that fine number crunching proving a Case Head and Pressure Ring "will Expand" under Pressure.

...

One question for you concerning all that fine calculating. As I looked at it, I didn't see any compensation being made for the actual "Primer" being in the Primer Pocket. Is it taken into consideration and I just overlooked it?

Never said that the case heads don't expand. Hot Core look at the pressures we are talking about to achieve ANY case head expansion! Over 70 ksi!!! That is just a tad over the top if one wishes to remain in SAAMI or CIP pressure specs.

Yes the primer is comprehended in the equation. It contributes very little as it is well beyond yield even at 11,000 psi. I has to be, this yielding is how it seals the primer hole. However, the primer cup can only plastically deform so much, and then it will ultimately fail. As you know the primer cup is supported by the case head, when the case head yields enough, the primer cup will ultimately fail (longitudinal tear). With the typical result gas escaping the breech i.e. blown primer.

ASS_CLOWN

AC,

What was the basic calculation for the charts?

I see the .223 cross sectioned, but didn't make the chart



Hodgdon website: 223 Rem, H335, 25.3 GR. 55 GR. SPR SP, 2.200", 24" barrel, 3203 fps, 49,300 CUP



Test: Ruger #1, CCI 400 small rifle primers, LC brass once fired processed from Scharch and prepped by me, 55 gr. Vmax moly, H335



pic left to right: unfired, 28, 29, 30, and 31 gr.





.223 case heads; unfired, 28, 29, 30, 31

Velocity and pressure are Quickload estimates

25.3 gr45,827 psi, 3142 fps extractor groove .329" 0% overload, unfired

28 gr, 66,064 psi, 3485 fps, extractor groove .329", 11% overload

29 gr, 74,496 psi, 3603 fps, extractor groove .329", 15% overload

30 gr, 86,492 psi, 3722 fps, extractor groove .3295", 19% overload .0005" expansion

31 gr, 99,405 psi, 3839 fps, extractor groove .3320", 23% overload .0030" expansion



Based on this, the limit for full hard .223 brass should be between 75kpsi and 87kpsi

Clark,

I have the dimensions off of that sectioned .223 case, but haven't run the numbers. I will try and crunch them up tonight.

By the way, I screwed around some more last night with the von Mises calculations, especially the spring rate of the cases part, and I think I have a fairly accurate model put together for determining an "average" spring rate for a given case head. The von Mises stresses have dropped a bit from my last post by using this new spring rate model as well. I also caught a stinking error in one of my formulas (Excel is f__ing great for that) which also contributed to some of the stress change. Anyway, I still have some work I want to do on the modeling, and if all goes well, Monday I will put it up in chart form.

From memory the outer fiber von Mises stress is 65+ ksi now and the inner diameter (primer pocket) is still around 120 ksi for the mauser.

After looking over a few cases and some notes dealing with measured case stretch before/after firing, I have deduced that each case needs it's own unique spring rate model (DUH that was a no brainer). Anyway, I have "averaged" if you will several case designs for each case head, to arrive at an "average" case spring rate. Truth is the compressive stress doesn't seem to substantially effect the outer fiber stress, but it sure does effect the inner fiber (reduces the hoop stress). In some cases the brass is so stiff that it actually has little effective thrust against the bolt face, believe it or not.

I am also not completely satisfied with how I modeled the compressive stress acting through the case head. I think I may revisit that as well. Anyway, give me some time and I think I can get the bugs worked out and put together a reasonably accurate simulation model. It may not be aweful user friendly, though (read NOT "Case analysis for DUMMIES").

If I can get it to reasonably well correlate with reality (which is the hard part since I am trying to make a generic model when in reality to be extremely accurate I must model each individual case design), and you can use Excel, I would being willing to share the spreadsheet calculator. Let me know. Like I said it will be rather knowledge intensive, but I can think of no better way to learn.

ASS_CLOWN

Clark,



Here are the results of the von Mises stress calculations for the 223 Remington case head.



Using mechanical properties for C26000 brass (cartridge brass)

Temper - H06



Tensile yield strength - 65,300 psi



von Mises stress at the Primer pocket surface - 117,186 psi

von Mises stress at the Extractor OD - 65,300 psi (initiation of yielding)



Chamber pressure - 86,427 psi (Nominal properties)

Chamber pressure - 80,809 psi (minimum properties)

Chamber pressure - 92,044 psi (maximum properties)



Again these values are ONLY valid for a H06 tempered C26000 case.



ASS_CLOWN



PS



The Mauser case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass is: 76,977 psi



The H&H magnum case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass is: 79,597 psi



The Rem Utra magnum case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass is: 83,950 psi



The H&H magnum case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass is: 79,597 psi



The 460 Weatherby magnum case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass is: 89,987 psi



The Rigby case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass is: 90,450 psi



The 7.62X39 Soviet case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass AND LARGE RIFLE PRIMER is: 66,769 psi



The 7.62X39 Soviet case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass AND SMALL RIFLE PRIMER is: 81,609 psi



The geometric and mechanical property tolerances for the C26000 H06 material and "estimated" case tolerancing provide for a +/- 7% value from the nominals I posted above.

Okay, I've read this thread a couple of times and while I am admittedly impressed, I'm hoping someone can dumb-down this issue for us non-tech types.

I gather that the moral of the story that ANY case head expansion is an indication of excessive pressure? Does the same hold true for PRE too?

If so, what's left to tell the average reloader wanting to work up a load when things have gotten too hot?

P.S. I started out by admitting I'm a dummy, so don't flame me for asking what may be a simplistic question!!!

No flaming on this thread at least not from me.

The moral of the story, and I admit this has gotten FAR more technical than I had ever desired to go, is that case head expansion occurs as a result of:

1.) Very high chamber pressures (far higher than SAAMI spec)

2.) Brass that is far out of mechanical or geometric specification ( WAY TOO SOFT or badly undersize)


PRE is a different animal. PRE is a result of the case expanding to fit your rifle's chamber; therefore, some expansion is expected. The degree of expansion is another issue, but suffice it to say with PRE you will be measuring a difference in diameter before and after firing.

If you are going to use the PRE method, I would recommend getting a very good cast of your chamber made and measure this cast in the same axial (lengthwise) position as you will measure your fired cases for PRE. This will allow you to understand better just how much your barrel is deflecting during firing. Barrels don't deflect that much, so if you are measuring increases of 0.002" or more you are probably dealing with some hot loads.

Common sense thing. Thicker barrels deflect less than thinne barrels.

PRE example (ASS_CLOWN Method).

Your rifle chamber cast measures 0.471" at the exact place that you will be measuring your cases for PRE. You fire off your cartridge and record a PRE of 0.4716". Let's assume this is a commercially loaded round, so we will call it our safety baseline.

You now fire off two hand loads.

Handload #1 measures 0.4715". This tell us it is ~ the same pressure (maybe slightly less) than the commercial ammunition.

Handload #2 measures 0.4721". This tells us this hand load is operating at considerably MORE pressure than the commercially loaded ammunition does. A wise man may decide NOT to shoot anymore of this handload recipe and opt instead to shoot handload #1.

In a perfect world, which we aren't living in, the PRE measurements would equate to actual elastic barrel deflection and you could calculate the pressure just like the strain gage systems do (well kinda). Let's just say you CANNOT do this and leave it at that. Otherwise it gets real technical again real fast.

ASS_CLOWN

Belaw, I'm having trouble even grasping the point of this whole thread. Best I can tell the message seems to be that if you load ammunition hot enough, you cause the head of your brass to expand and flirt with case head separation or push a little harder and you can have catastrophic failure of the action!

Duh???????? OK. I've known this since practically day one of my reloading career. I don't give a hoot in hell for all the formulas and angles of the dangles that are being babbled about here.

Rather than teach some BS course on the mathematics and pressures involved here, isn't it just a hell of a lot easier to avoid the problem?

This philosophy has worked for me for 45 years and dozens of different rifles and pistols. All anyone really needs to know is what every loading book in the land tells us on every page: Approach maximum loads with caution.

Works for me. Going beyond the point of common sense is like trying to see how far out on the ice in a frozen river you can tap dance. You won't like it a damn bit when you reach the critical point.

Maybe Ass Clown has never seen a blown up rifle. I've seen a few and talked to the guys who blew them. They didn't enjoy the experience. They all trashed a good gun and most had some scars on their body as souveniers.

Some shooters aren't so lucky but obviously I didn't get to talk to them.

The moral to this whole tortuous thread is simply pay attention to your gun and ammunition and keep things "within the borders" of sensible reloading.

Pecos,

You get an "A"! That is exactly what I am trying to say, if the case head expands (CHE) you are WAY over pressure.

I am impressed, and you said you did not have a clue what all the techno mumbo jumbo was about! You old BSer you, you knew all along, didn't you.

CHE (case head expansion), in my opinion will get you hurt, your firearm hurt, both, or worse yet, killed.

ASS_CLOWN

If I read these numbers right,that's a big IF,he pointing at roughly the point at which you get loose primers,depending on brass lot.

Amen, AC. It will for sure get you hurt and wreck a good gun or even do little subtle things like set the lugs back a few thousands to sneak in a little headspace into the equation.

I remember when I was flight instructing years ago. We taught stalls...but not how to train pilots how to become experts AT stalls...simply to recognize the symptoms leading up to a stalled condition and how to avoid it.

Anyone swelling case heads is going where angels fear to tread.

Downwind, I'm not sure loose primers is always an indication of high pressure. I would almost always interpret loose primers as a sign of high pressure........BUT.........

I give you the curious case of a rifle I used to have. It was a .458 x 2" or 458 American as it was called then. It used magnum brass and I had HELL getting any great case life from this gun, regardless of the brand of brass.

After 3 or 4 rounds the primer pockets had expanded where I could seat the primer with my fingers and by the next reloading, the case wouldn't even HOLD a primer.

What makes this a real mystery to me is I was shooting a 350 gr cast bullet with 20 grs of 2400 behind it. There was NO high pressure!

What the hell was happening to my primer pockets? I don't know to this day. Fired primers were always rounded after firing with absolutely no sign of any pressure to speak of at all. But my cases died all the same.

I fired an almost identical load in 30/06, 20grs of 2400 behind 205 gr cast bullet and I couldn't wear cases out!

Is there something about magnum brass I don't know? Does it have some strange proclivity to blow primer pockets?

Only thing I can say is almost all my brass was once fired and had thus endured ONE firing at Magnum pressures. It was too easy to make my own cases from other brass and I was too cheap to buy new.

Well, it has gotten to be quite a technical discussion....

belaw, my bottom line is the same as AC's, but for a slightly different reason. He used engineering calculations, and I used the industry standard methods for evaluating measurement systems, and neither PRE nor CHE will reproduce the same output number, given the same input pressure. Both systems give some information, but it is mixed with so much random noise that they are quite unreliable.

There is one poster who always hops on, and says he's been using them for years and years, and that they are fine, and he knows because he uses them, yada yada... no data, no physics, no calculations.

Don't use either method. They are unreliable. They can easily give you the illusion that they work, since you will probably not blow up a gun, or get gas in your face, whether you use them, or pick a reasonable random number.

It's kinda like the old joke about why they put 'In God We Trust' on pennies.... it's there for people who use them for fuses.

Hot Core = no data, no physics, no calculations, no evidence of any kind.

Hot Core,

Doing the math, is nothing more than performing a great deal of work to illustrate the obvious! It is simply amazing how much math is done by many to this end.

The truth is some people think in equations and mathematical terms, I am one such freak. The math actually helps me understand the boundaries of the playing field. Because I had done the math (read homework) I was once able to collect a considerable amount of money from some, not so well educated, gentlemen who said I could not fire a full house load in a certain big bore if I had annealed the cases. I did yield the web, but they said I would blow the primer, which I did not and thus won the bet. The pay-off more than compensated me for the screwed up cases (had to fire off 10 to prove some statistical significance).

ASS_CLOWN

AC,
I have been designing switching power supplies for 25 years, with lots of math. For me math is useful for sizing parts and predicting speed, etc., but there is a limit to what can and should be designed, and beginning of what should be found empirically. That threshold varies with the individual, but my knowledge of the math of extractor grooves expanding seems within reach, if you just hand it to me on a platter.

The only thing math ever did for me was give me a headache.

Clark,

What exactly are you looking for?

ASS_CLOWN