You asked, I have an opinion.
There are several signs for pressure. One classic pressure sign is "primer metal cratering around the firing pin". Some are more reliable than others. For example, I shoot Federal primers, they are notoriously "soft". I get primer cratering with moderate loads and no other pressure signs - it's a red herring. If I make a load using Federal match primers and they show cratering, I don't worry unless I also have another sign. I have owned weapons where the firing pin hole in the bolt face was a bit large. That will always crater Federal primers without other pressure signs and may crater harder primers.
I own a brand new box of federal gold medal match 223 brass. In my weapons, with my standard loads, case heads expand after one shot. Please don't misunderstand, I am not picking on Federal - I use their primers for all precision work and I am happy with their products and I recommend them but I don't shoot that brass in my gas guns and I know to ignore cratered primers.
In some guns pressure signs show up all at once, in other guns they show up in a sequence - first sign 1, then signs 1 and 2, and so forth. If I see one reliable sign, I see yellow lights and I pay close attention. If I see two or more signs, red lights start blinking. When I see difficult to extract and case bases expand, I know that something bad just happened. If the bolt won't close on a piece of brass I just fired, something bad just happened. If the primer pockets won't hold a primer then I was a bad boy. Here is my list:
- difficult to extract, for an unfired round, can also be bullet seated too long
- case head expansion, measure the rim and and just above the extractor groove.
- Case separations, head or body, can also be caused by bumping the shoulders back too far.
- cratered primers, check primer brand and firing pin hole in bolt face
- Primers smashed flat, can be caused by soft primers and (maybe) by making the flash hole too large.
- pierced primers, can also be caused by not seating deep enough and firing pin protruding too far and
- Case head ejector hole marks might be (a) too much pressure for this brass, (b) burrs around the ejector hole (c) you annealed the case head. Never anneal the case head. I have been told that some people get ejector marks if their brass is too short or too long. I haven't seen it but there you go. Try different/harder brass.
- "no-go" gauges that "go"
- unexpected rapid disassembly - sort of the ultimate sign.
I once accidently made a batch of 300 win mag using heavy bullets and 10 grains too much H1000 powder. There was much noise, flash, and recoil. The excess gas from my brake blew stuff off my shooting bench. I had to hammer the bolt open. The case was wrecked but the gun was fine. It didn't have to turn out fine.
Does accuracy matter to you? As you push the pressure, how does the gun group? With very few exceptions, very hot loads don't group as well.
Does case life matter to you? If you have an unlimited supply of brass, you may not care about brass life so long as the case is intact enough to eject. Otherwise, as you are testing, you might keep using the same few pieces of brass and see how long they last.
Does barrel life matter to you? The velocities that go along with relatively high pressure erode the throat. Guns with eroded throats shot bigger groups. If it didn't matter, benchrest shooters would not swap barrels every 1,000 rounds.
I saw two guys blow up their guns - this is yer basic "unexpected rapid disassembly". Both were a messy. And the guns were wrecked too. The first guy was scalped and the second guy looked like he had been used as a 40 yard shotgun patterning target. If you are going to run very high pressure, you might want to buy a no-go gauge and check your weapon as you test. Chances are you will see other signs first but when you get above 70,000 PSI things start to happen pretty fast.