Thank you Channing.
re: the effect of bulging prior to the burst on wall thickness. I discussed the issue with the Metallurgical Engineer doing one of my failure evaluations. His answer was "not much".
Helpful demonstration.
The straight ribband end welds are marked.
The crack clearly occurred at the rod to rod weld.
The terminal cleavage/split was
across the welds.
Damascus mythology has been that barrels will "unwind like a slinky". Not if the ribband welds are intact.
