I'd be interested in polling the group as to what PSIs they believe the various classic pressure signs occur. For example,

1) At what internal PSI do primer pockets begin to loosen fairly rapidly - resulting in maybe only 5 case reloadings before the pocket is too loose to hold a primer (i.e., the primer can be easily pushed back out by hand)?

2) At what internal PSI do extractor marks occur?

3) At what internal PSI would a primer pocket "blow" in a never-before-fired case - that is, the primer pocket would not be usable for a second loading and at firing gas would escape?

4) At what internal PSI would you get a black ring around a primer?

5) At what internal PSI do primers flatten?

6) At what internal PSI would the firing pin crater evert past the base of the primer?

7) At what internal PSI would the case head separate, when fired in a well-constructed bolt-action rifle?

Any thoughts. Regards and safe/happy shooting, AIU

I usually find that primer pressure signs don't occur under 45,000. At 55 they're flat and sometimes the firing pin hole is notices. Sometimes you will get soft brass that will have the primer pockets enlarge after just a firing, so unless it is a bunch of loads showing loose pockets, it may be soft brass, Extractor marks mean back the hell off, and head seperations mean you did'nt back off

We need to look up some of the experiments that Clark Magnumson performed on different cartridges. Lots of very good information.

By the way, waiting for "over-pressure signs" is what gets people in trouble when loading the 45-70 for leverguns. I.e. you don't get any pressue signs until you are way, way over-pressure.

pressure signs can be tough to interpret. IF you do not lighten the ejector plunger spring, and nk size or PFL size such that the case is forced against the casehead, the ejector marks will show up in even loads quite shy of max in the manuals. Now if they are INDENTED and 3 shades shinier than the brass itself, then THAT means back the hell off.

It's amazing how little we seem to know about this topic - yet, we all reload on a regular basis.

Buchlok; In a dry chamber the case will not move back against the breech until about 40,000 psi or so. With headspace primers will project up to that point, when the case comes back they will startr to "rivet".
This will be an interesting thread if people contribute. Once the case head expands or the primers loosen it shows that you are reaching the yield point of the brass. No matter what the load, a smart person will back off at that point.
Good luck!

I will let you know in a couple of weeks. I am currently trying to work up a load for the 22-250 AI. What I am doing is loading one round starting at midrange of the minimum and maximum load and increasing each load by a .5 grain to .5 gr. over the max. for each powder. I am trying W760 and H414. I will be looking for a certain velocity and pressure signs as I shoot through the chronograph. I probably will see flaatened primers before the difficult bolt lift since this is an Ackley Improved. What I am trying to say is that I couldn't work up a load without a chronograph.

The diamentions of the chamber, cases and roughness of the chamber wall will have an effect on how soon pressure signs appear. The primers will flatten with excessive headspace or in a action that flexes easily, some single shots and levers come to mind, before they will in a strong bolt gun with proper fitting cartridges. The cases will also show signs of sticking in these actions with lower pressure.
I`ve read here and in other places that brass starts deforming and pockets start expanding around 75KPSI. I`ve never had a blown primer or case failure (knock on wood) so this is all second hand info. I have stuck a few handgun cases though and know the pressures were far lower then rifles would produce.
I don`t believe there is a set or even a general pressure that one can say you can expect pressure signs or brass failure. There`s just too many variables.

Guys, I'm asking for SPECIFIC PSIs. Some may have actually correlated these "classic" pressure signs with corresponding MEASURED PSIs with either a strain-gauge or piezo-electric transducer system. If you have such data or know where it is published, please share - I believe all of us would benefit this info.

In the meantime, I'm going to suggest answers, which are based on QL + chronograph data and discussions with various manufacturer ballistic technicians.

Suggested PSIs at which the various classic pressure signs occur are as follows:

1) At what internal PSI do primer pockets begin to loosen fairly rapidly - resulting in maybe only 5 case reloadings before the pocket is too loose to hold a primer (i.e., the primer can be easily pushed back out by hand)?

[Noticable pocket loosening begins at ~65,000 PSI and accelerates with increasing pressure until a totally loose pocket develops after one firing - that is , a blown primer.]

2) At what internal PSI do extractor marks occur?

[Well-developed, bright extractor marks develop at ~70,000 PSI. But, some bolts don't show extracter marks easily (e.g., M70), whereas others develop extacter marks quickly (e.g. R700).]

3) At what internal PSI would a primer pocket "blow" in a never-before-fired case - that is, the primer pocket would not be usable for a second loading and at firing gas would escape?

[Beginning at ~75,000 PSI and almost always at ~80,000 PSI.]

4) At what internal PSI would you get a black ring around a primer?

[Just before a blown primer, ~75,000 PSI.]

5) At what internal PSI do primers flatten?

[Variable and difficult to know - unreliable pressure sign, because its gun dependent. But, it should be considered worrisome.]

6) At what internal PSI would the firing pin crater evert past the base of the primer?

[Variable and difficult to know - unreliable pressure sign, because its gun dependent. But, it should be considered worrisome.]

7) At what internal PSI would the case head separate, when fired in a well-constructed bolt-action rifle?

[In a well-constructed, tight bolt-action rifle this must be beyond ~100,000 PSI, possibly as high as ~150,000 PSI. Usually caused by substitution of the wrong powder (i.e., fast for slow powder) or obstruction.]

Any thoughts or differing opinions?

Regards and safe/happy shooting, AIU

People are starving over the world, dying every day - and you have enough to feed the trolls copiously. A shame.

*Shakes head*

Carcano

quote:

Originally posted by carcano91:
People are starving over the world, dying every day - and you have enough to feed the trolls copiously. A shame.

*Shakes head*

Carcano

Say what??

Carcano91, explain yourself. If you have something to say, say it. Where are you from?