You're welcome Drew. I'm going to say that it would be darn near impossible for even a PhD Metallurgical Engineer to provide a formula to accurately quantify the amount of thinning that would occur in these scenarios. There are just too many variables that wouldn't easily be repeatable or reproducible. A big factor is simply knowing what the actual pressure curve in that region was when it blew. I think we can safely say... "too much!"
If we could know the near instantaneous pressures involved, a guy with those credentials and that sort of training might be able to give us a good ballpark estimate. But a different barrel sample, even one made from the same heat of steel, that had some small internal flaw or inclusion, could throw his calculations way off one way or the other in a real world test. That wouldn't necessarily make him wrong. It would demonstrate that we are working with a material that is not 100% homogeneous and free from impurities. We also have engineering tables for accepted loads for framing lumber, for example. A hidden knot or bark inclusion can throw off the safe ultimate load there too. When the engineer at METL told you "not much", he gave you good information, because the difference between the thinnest point, and the dimensions just before and after was only .006"
Another steel that had different qualities of composition analysis, tensile strength, actual Rockwell hardness due to work hardening during rolling, etc., etc., may have stretched a bit more or a bit less before blowing out. But I think it's safe to say this barrel was doomed by the obstruction, and a shooter who didn't know about it. Like Lloyd, I too am interested in hearing what the actual analysis of this barrel is.
