Doc06;
The hoop stress, along with the strength of the steel, is what determines how much the bbl can contain without either bulging or bursting. Also to go even further there is also a certain limit which if exceed can lead to fatigue failure. Steel is normally rated for an "Ultimate" & Yield" strength. The yield point is where it will be permanetly elongated (bulged in case of bbl) while the ultimate is the point at which it will rupture. Below the yield point is the fatigue point above which constant motion will eventually lead to failure, as in bending a piece of wire. Understand as the charge goes down the bore, with the gas pressure behind it, the bbl actually swells slightly but as long as the yield point (also sometimes called the elastic point) is not exceeded it will return to normal. Thus if the ultimate point is exceeded the bbl will burst, if the yield is exceeded it will bulge, while continiously exceeding the fatigue point will eventually tresult in a break, often a crack which doesn't show signs of high pressure failure etc.
The only "Fly in the Ointment" is for older steels & particularly composite bbls we simply don't know with accuracy just what all those points are. For modern steels these are all worked out in metalurgical labs. During my career as a machinist I was on some occasions relegated the job of preparing some of these test specimens for the "Met Lab" to test. We had several types we made & tolerances were vere close.
