Drew,
What I was trying to address with my remarks on pressure has nothing to do with a failure, catastrophic or otherwise, rather it speaks to the effect of long term use of improper [overly high pressure] loads in old guns. For example, I have held & examined minimally hundreds of older Damascus bbl'd. guns in my lifetime that were relegated to 'wall hanger' status because they had been 'shot loose'. All of the same guns I'm speaking of had their Damascus bbl's. still in tact even if dented, heavily corroded inside, ribs loose, hooks reattached, forearms wired on, stocks cracked/repaired, &c. Empirically, that suggests much better integrity than today's wives tales give them credit for & I'll leave it at that. Back to the pressure thing and the low tensile strength mild steels most, if not all, older double guns were made from, they get 'pounded' excessively when using high pressure rounds to use the vernacular and the result is the same thing as plastic deformation, if I'm not mistaken. Another descriptor that can be applied to low tensile strength mild steels is they tend to be more 'malleable' than high tensile strength alloyed steels, i.e. more readily deformed.
When we examine an older double gun, we have to realize that even if the frame was properly case hardened, that there is no guarantee that the hinge pin, the barrel lump or even the opening lever's spindle and bolting was ever hardened at all, possibly leaving those components subject to excessive pressure deformation, over time.
Best, tw
BTW, this is not intended as any form of rebuff should it read that way, rather another attempt at better clarity on my part.
