9MM Standard Pressure, as layed out by SAAMI Specifications is 35,000 PSI. +P Is maximum 38,500 PSI.
This does not mean your gun will "blow up" if you exceed these specifications by 1 PSI. All this means it is a recognized "standard" for loading ammunition for 9 MM. If we were to test pressure rounds in every different gun, we would see each gun failing due to high pressure at different points. Nobody knows what these points are, but we have some ideas based on history of people trying different things, to "understand" guidelines of what is somewhat dangerous, dangerous or very dangerous. It should be noted that many people are scientific in the way they approach these questions. So some people, test very high pressure loads just to see what will happen. What will failure first in a mechanical apparatus, is the weakest part because energy will travel in path of least resistance. In other words, if we have a mechanical system with 1/8 inch thick hardened steel, then we have a piece of brass that is much softer metal, much less tensile strength and its only several thousands of an inch thick? What do you think is going to have the propensity to fail first? The brass is generally "a" weak point in this system, or more notably in this order: Primer failure (flattened, hole, blow out), Case failure (bulging, cracking, case head seperation), the slide stop or slide in a gun will crack from very high pressure or having wrong recoil spring, etc. People on the net talk about "blowing up" or "don't blow your face off" or etc. But has this "ever" happened? Or is this just a rumor because they read "NEVER EXCEED MAXIMUM CHARGES!!! EXTREMELY DANGEROUS" on everyone's site and are conditioned to think that its super dangerous? We are not talking about having something "impede" the barrel, then firing a shot. Obviously that will blow the barrel to pieces. You cannot stick a potatoe, or have another round inside the barrel then fire a shot, you will split the barrel and destroy the gun. So the question is? If SAAMI spec is 35,000 PSI, and I load up some ammo that is 45,000 PSI, will I hurt myself? Our opinion, and that is all it is, from our experience, is that it causes primer blow outs, split cases, case buldge (we are talking about supported chambers only, not Glocks with standard barrels, etc). If you watch 9 MM Major people, like we do, you will see they shoot "hundreds of thousands of rounds" (many of them, combined) in ranging pressures that are estimated to be 40,000-48,000 or so PSI. We think normal is around 44k psi. What problems do they have? Ask them. Any guns ever "exploded"? Anyone ever hurt? They have frames cracked at the stop area from the slide hitting the stop so hard. They have blown primers, holes in primers, cracked cases, buldged cases. Barrels cracked? Blow ups, as in the gun explodes and shrapnel imbeds in your face or takes out a piece of your head? Not that we are aware of. That doesn't mean it can't or hasn't happened. We think this, and its simple. YOU are responsible for whatever you do. If you "choose" to load up something more than any manufacturer recommends, then the burden is on you, and you only. Please, don't put other people at risk around you, if you want to act stupid, please don't do it around other people. This kind of thing can get people hurt. Please be safe and work up for all loads.
Since we don't have a lab, and we don't want to pay a ton of money to send rounds to a lab, what is a method for evaluating high pressure? This perhaps, is "a few" ways to do it.
- Use the same primer brand, and stick with it. Uniformity is key.
- Deprime the primer from case, and measure its diameter. Does the primer now appear with higher diameter because the top of the primer face has expanded (flattened)? It is by this measurement you can get an "idea" of what is higher pressure. The larger the diameter, the more the pressure. This is similar to the CUP pressure test. CUP is basically a copper disk, that is crushed against chamber to see how much it compressed. The more it was compressed, the more pressure. This is the same logic here except for one thing. It assumes the primer metalic composition is as consistent as pure copper like the CUP test blanks/slugs. Its probably not, but its enough to make comparitive judgements perhaps, expecially if you evaluate say 10 at a time, and see extreme spread of measurements between various loads.
- Measure the expansion of the brass case at the base versus before it was fired. The more expansion, the more pressure generally. This also makes the assumption that even the same brand brass that weighs the same, as the same strength in the base area and is consistent piece to piece. It is consistent "enough" to make judgements, we think.
So lets take a look at some primers before and after, and some brass before and after and get an idea of what is going on with pressure. We can then correlate these 2 things together and make a judgement on whether this load was higher pressure than another. This works for us, but is not done under strict controls in a lab, so if you choose to use this method, that is your choice. We choose Federal Gold Medal Primers because this is the softest primer we could find. They flatten much more easily than CCI or Fiocchi. I do nto know if it is design by Federal, or what, but these start to flatten and exceed .1745 diameter or unfired, when they get near the ~35k PSI area. This is a really good design, if it was intentional. We find that a normal primer expands/flattens to about .178 for 9MM Major loads we tried, on average. Some are .177 and some are greater than .180.