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

Rubbish.

C.

Except for 5 and 6, which depend on the primer cup as much as on pressure, that you'll see all of those signs once you've gone past safe limits. When you see one, go back.

Beyond that I think there are too many variables to even begin to categorize things based on damage to the case.

Okie John

quote:

Originally posted by okie john:
Except for 5 and 6, which depend on the primer cup as much as on pressure, that you'll see all of those signs once you've gone past safe limits. When you see one, go back.

Beyond that I think there are too many variables to even begin to categorize things based on damage to the case.

Okie John

My sentiments exactly!!

Sorry, El Deguello.
You are dead wrong here.
And upon rethinking, you'll certainly find out why. You don't need me for that, do you?

Carcano

Cancano91, explain yourself - if you've got something the group will benefit from, provide it. Taking cheap shots for the sake of taking cheap shots is CHEAP.

once again,..ejector marks are unrelaible unless they are super bright and indented into the casehead. I have seen MANY MANY rifles which whne firing factory ammunition (lawyer ammo) that leave ejector marks. These loads have never even shown a chrono reading that was so much as close to over pressure.

Next, brass tensile strength negates that as well. Manufacture 1000 cases to exactly the same hardness and run them up the ladder until they show pressure signs. Now,..manufacture another 1000 cases to another hardness, and run them up the ladder until they show pressure signs. Neither case will have been at the same pressure, even fired from the same rifle.

If all cases were the same hardness from every manufacturer, then the test would hold some value, but until then, it is all speculative.

Now, another variable, ejector spring tension. Take 2 rem700's next to each other with consecutive serial numbers in same caliber, then run them up the ladder. neither rifle will show pressure at the EXACT same load and seating depth given factory barrels being cut by a reamer until it is dull enough to sit on top a stick of hot butter and not sink in.

Pressure signs show up when your chrono says they are too fast. AND even that is inconsistent. I have a sako action with fixed ejector that ran 140gr pills to 3200fps in a 26" tube in 6.5-06AI with absolutely NO signs of pressure. The primers were barely even starting to flatten, but LOGIC dictates that the pills should NOT be that fast in that barrel with that caliber in that bullet weight. LOGIC and UNDERSTANDING tells you you you are too high,...but to the untrained eye, and with no chrono, danger follows.

Suggest you buy "rifle accuracy facts" by Harold Vaughn and then some more books on internal balistics for a better explanation. THERE IS NO SET RULE,..every rifle is different.

In order to even begin to prove or disporove any THEORY or opinon, you will be working the rest of your life to afford the equipment to even begin the experiment. Also,,without a test rifle that uses the same hardness brass, with bullets of all the same jacket alloy, with the same burn rate powder, and the same lot of primers, and the same barrel (with the SAME ROUND COUNT EVERY FIRING) you are farting in the wind.

2 eyes and an understanding of pressure is the teacher, everything else is speculation. I can say that XXX grs of powder does it in my rifle with thus and such brass and thus and such bullet,..but your rifle with a different lot of powder, different lot of bullets, and different lot of primers, even from the same manufacturer, will show completely differnt results.

I can run my lot of win brass to 5000psi more or less than yours and experience the same results. It's all relative. Good luck buying all the equipment, and let us know how much it will cost to rent it for our own experiments to help you pay it all off.

When you have a loose primer pocket the first firing, or blow a primer, you are too high. If you have a black barrel and crown after one firing, you are too low. Real simple, and hardly mysterious. Leave the "who cares" measurements to the ivy league labs and await their results.

Not to flame,..but the question itself is somehwere in the realm of a 15% ERROR at best. I've been on both sides, too high and too low. Every loader learns his rifle and it's limits, but even a match grade barrel on 2 different rigs shows 2 different results. If it were as simple as a value given to pressure, then the value given to load data would be set in stone and never deviated from. And how much fun would that be?

Lets not forget yield strength on various actions, and bolt lug differnces, as well. These yields all add to primer appearances as well as firing pin spring tensions and their affect on primer strike appearances. So much for primer cratering as an indicator as well.

I'm not sure answers exist to your questions and I wish they did...it could help us all.
Many of today's high powered cartridges fired in modern bolt actions run about 60,000 PSI or there abouts. It's my personal feeling that many Ackley improved owners are handloading to the start of these pressure signs and backing off slightly and that those pressures are between 65,000 and 70,000 PSI. Further I believe that the evidence of any of these signs is an indication that one's pressures are in excess of 70,000 PSI.

I have just posted opinion.....not fact but I doubt that real data exists for your questions.

Thanks JustC, that's a nice response. But, is it possible to put a RANGE of PSIs that might correspond to roughly when the above pressure signs occur? Thanks Vapodog - I would agree with your PSI RANGEs. Regards and safe/happy shooting, AIU

AIU, I would venture a SWAG at somewhere around 62,000-7x,xxx psi. I think a strain guage attached to the rifle after being completely trued, and values given to brass harndess, and jacket alloy hardness, ejector spring tension value, as well as land/groove dimensions taken, you could BEGIN to formulate it.

Next, after pressure signs are recorded and the strain guage gives the pressure reading at which they showed up, the formula can be changed to determine the variables and their contribution to pressures. First, change ONLY the brass hardness and run the ladder again until pressure signs show, then record that strain guage reading. Next, go back to the original brass hardness, and change the jacket alloy harndess. Run the ladder again until pressure signs show, and record that strain guage reading. do this all the way through with all the variables only changing one per experiment, but keeping the chamber size constant. That is the "control" of the experiment.

After this has been completed, you can start to develope a formula with values given to every variable and then make the scientific formula itself. Then and only then, could the shooter determine AHEAD OF TIME at which pressure his rifle and load combo would show signs of pressure, and he would NOT need the strain guage. This would however mean that you would have to gain the hardness readings of your components as well as land/groove dimension, and spring tension first, and then insert them into the formula to arrive at the value at which your cases will show pressure signs in your rifle with your selected components. When they appear, you will know exactly how high you were on that load, cause you figured the value first, and then ran the ladder until the evidence appeared.

every time a component is switched, you will have to get it's hardness rating, and then re-run the equation for the new final pressure value. Also, remember as brass gets work hardened, the values will again change and the brass will need constant monitoring for changes in hardness/pliability. Just the same as BC changes over distance as speed is decreased.

JustC, what's a SWAG?

The following are my suggested 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

JustC, GREAT REPLY!!!!
AIU....."SWAG"...."Scientific Wild Ass Geuss" GHD