I seriously doubt it was a cook off either, but did mention it. I have seen one in my lifetime & that was on a 1,000" range with a .30cal MG, forget the model but was .30-06. Operator left it loaded at cease fire rather than opening the bolt & putting in the T-block. We were all back down off the firing line getting instructions on the next order of fire when she let go, so was a few minutes. He got one Royal Chewing out & NO it wasn't me.
I really had not thought about build up of blows incurred from inertia but that could also be a possibility, was simply thinking the hammer had to fall.
I had one double go off in closing once, & old J Stevens. All I could ever detetermine was I didn't open it quite enough to get the sears fully set & was in my early years & closed it rather swiftly. After that I always made sure I fully opened it & closed it more gently & it never did it again.
