I'm still trying to understand why my 30-06 muzzle didn't get blown up by those 105+ksi spikes, if they are real.
Hatcher's Notebook provides some clues. He mentions that he "used pressures up to 130,000 pounds without any apparent ill effects on the barrels." [note: he probably means 130,000 CUP, which might be more in PSI, but I'll use PSI for my calculations]. He tried turning the barrel down to 1/8" wall thickness at the chamber, and firing it with regular and high pressure cartridges. As the results were not visible, [he] turned the barrel down so that it was only 1/16" thick over the chamber. It held three regular service cartridges perfectly. [He] then put a 75,000 pound shot through which blew a piece out of the side......"
I don't have a Springfield handy, so I'll use my M700 barrel dimensions instead and estimate the stresses created in Hatcher's experiments at the chamber area where my strain gages are mounted. The stress numbers are for the tangential stress only, and I was too lazy to make a seperate calculation for the brass case so I treated the brass as if it were 4140 steel. This shortcut will result in my calculated stress being only slightly smaller than the actual stress.
58 ksi load, standard barrel = 75 ksi stress inside, 17 ksi outside
130 ksi load, standard barrel = 167 ksi stress inside, 37 ksi outside
58 ksi load, 1/8" wall thickness = 113 ksi stress inside, 55 ksi outside
75 ksi load, 1/8" wall thickness = 147 ksi stress inside, 72 ksi outside
58 ksi load, 1/16" wall thickness = 162 ksi stress inside, 104 ksi outside
75 ksi load, 1/16" wall thickness = 209 ksi stress inside, 134 ksi outside, and it finally blew up
If Hatcher's barrel steel had a 100 - 115 ksi yield strength like modern 4140 barrels, then we can say that his barrel did not fail until the stress on the outside surface of the barrel exceeded the yield strength. If that is a general rule for predicting barrel failure, then my muzzle may not come unglued until the spike hits 180 ksi.