coyota1 comments:
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Guns are proof tested for twice the pressure their pressure limit rating I believe.
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Twice is a bit much, I think.
Proof loads are typically 25 to 40 percent above normal average peak pressure. For example, the 5.56 M193 has a maximum CUP pressure average of 52,000 CUP. The 5.56 M197 proof load has a max standard pressure of 70,000 CUP; a 40% pressure over standard ammo.
By comparison, the 7.62 NATO and .30-06 round has 50,000 CUP max average pressure and their proof loads are 67,500 CUP max average; 35% higher for the proof load. Some 7.62 NATO handloads the military teams use in matches are at proof load levels for M1, M14 and AR10 service rifles. I've shot them and they do let you know they've got more gusto than standard service ammo.