Yeah, it's a bummer when you can't hold the bulge in and it blows up a head on the shooter - and it all happens so fast.
You're very right 2-piper to mention the yield strength as the first pressure to be worried about inside a barrel. For the gun's sake.
Yield strength being that strength at which the steel first deforms with permanent damage, it is always below the maximum tensile strength where, of course, things break because we pulled too hard on them. To give ballpark figures on what yield strength is, simply consider that for high strength steel, yield occurs at about 90% of the maximum burst pressure. For medium steel, the yield occurs at 80% already and for really soft steel, the permanent bulging will start readily at only 60% of the maximum-break-everything pressure.
Most guns fall in the lower-medium 80% bracket, but it depends. Some modern guns are made of high strength steel and the guns discussed in this topic fall in the low range. Damascus does not fall far below the value for my special Mannesmann.
So in my example, we had
unsafe blowup pressure at about one inch beyond the chamber: 21000 PSI
unsafe pressure at which bulging deformations are permanent at 60% since this is a low strength steel barrel to begin with: 12600 PSI
derated to a 50% safety factor which would mean we are just seemingly 10% away from damage - really thin margin for loading errors: 10500 PSI
derated to a 40% safety factor leaving a breathing room of 20% now: 8400 PSI
derated to a 30% safety factor leaving a breathing room of 30%, this is 1 to 2 margin, now: 6300 PSI
The pressure to aim for depends on the risk taking comfort of the operator.. Good call.
