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Overpressure
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The appearance of the primer as any kind of 'pressure gauge' is urban myth.
I would strongly disagree with you on 9,40,45. Most auto pistols leave a swipe mark that increases through the normal safe range and gets much bigger just above safe loadings.
Instead of arguing, load a few levels of charge through the safe range and compare to factory ammo. I think you will see it. That said, it depends a lot on the pistol used. 1911’s show nothing, IME.
I think this has more to do with the gun trying to unlock too soon (too much muzzle momentum for the design) than it does to to with actual pressure.Most auto pistols leave a swipe mark that increases through the normal safe range and gets much bigger just above safe loadings.
There is nothing wrong with those primer pics. I have a S&W 9EZ that leaves a similar impression on the primer. Emailed S&W and they said there is a reason it does that - it was a required relief so the firing pin would not break. Take a look at the firing pin area of the slide. I think you'll see why it does that. It's normal.
Most auto pistols leave a swipe mark that increases through the normal safe range and gets much bigger just above safe loadings.
I think this has more to do with the gun trying to unlock too soon (too much muzzle momentum for the design) than it does to to with actual pressure.
There are two different kinds of "swipe marks". The kind caused by too high pressure shows on the primer AND the base of the case. Its uncommon.
The other kind is very common, and only shows on the primer, and is the result of the design of the gun, and has nothing to do with the pressure.
It is due to the firing pin not being retracted before the barrel starts to unlock.
My Sig p220 (45acp) does this. It is normal. Lots of modern pistols do it. My 1911s, don't do it. Their design is different.
I think this has more to do with the gun trying to unlock too soon (too much muzzle momentum for the design) than it does to to with actual pressure.
The more I think about it,I think you are right. I’m seeing correlation not causation.