I think your 'bulge' observation is correct Drew.
This would appear to not be an over pressure caused chamber explosion at all.
My vote would be something stuck in the forcing cone.
I might be misunderstanding you but, whatever caused it was an overpressure issue, whether an obstruction, an overcharge, whatever. From the photo I see that left primer shows signs of high pressure. High pressure is the direct result of an obstruction. If, however, it
was an obstruction, IMO it had to be directly in front of the chamber. The "common scenario" I can come up with for that is a base wad being "sucked out" of the case an lodging there. And with the Gun Club hull, it can't be a loose base wad as they are of unibody construction.
One possible scenario would be this: Powder bridged causing a double drop, the shell with no powder just ahead of it on the press was used in the left barrel just prior to the blowout leaving it's wad in the forcing cone, by sheer "luck" the next shell loaded in that left chamber was the double charged one. Combination of an overcharge and a forcing cone obstruction equaled what we see. One would think that if this had occurred the shooter would have noticed the blooper and checked the barrel, however. This is all conjecture, of course, but within the realm of possibility. I know where there is a Boswell that blew almost
exactly like this, and it was caused by too hot of a reload.
SRH
