David;
When figuring the strengths of steel there are several factors which are involved. The two which holds the most interest to us here are Ultimate tensil & yield tensil, some times referred to as the elastic limit. The ultimate is of course the point at which the steel will break or in our case burst. The yield is the point at which it will accquire a permanent bulge. When pressure is applied inside the chamber it will "Swell" slightly, but upon removal of the pressure will return to original size. pon the pressure reaching the yield strength it will immediately take a sudden increase in its "Swell" & will not return to original size upon removal of the pressure, thus bulge has resulted. If the pressure is high enough it will of course continue to swell until it reaches the bursting point. Now lets assume that by knowing the yield strength of the steel we could then calculate that the pressure required to stress a given chamber to its yield point was 12K psi. "Theoritically" then we could fire a million rounds @ 11K psi with no detrimental effect. However another factor rears its Ugly Head, this may not be the correct technical term, but we have to consider the "Fatique Factor". This is simply saying if we go too close to the limit for too many times eventually the steel will just "Get Tired" & fail even though we never actually reached its failure point. This is of course one of the major reasons why service pressure is only a fraction of proof pressure. The best advise I can give is to simply keep ones loads within the service pressure for which the gun was designed.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra