I find the pic of the hull from the failed bbl. most interesting. It would appear that the cleaner green area w/the jagged tear was in solid contact w/the chamber wall at the time of failure & the 'less green' or 'frosted' portion was subject to burning powder gases [blow back?]. I would find that consistent w/Joe's observation of an expanded head at the uppermost head's [or 'brass'] edge. The fact that the torn area or 'clean green' outer portion of the hull does not show any signs of escaping powder gases is perplexing.
FWIW, I recently fired a 20 ga. Remington G.C. hull [previously several times reloaded] in a 12 ga. gun. It was NOT intentional. I have retained that fired hull. There are some similarities to the hull's outer appearance. My fired 20ga. Remington C.G. hull clearly has an expanded edge at the top of the head and also exhibits similarities in it's outer hull surface being 'frosted' in appearance and the mouth being split in several areas and clearly 'brittle'. I consider myself both lucky and fortunate that the Remington hull was sufficiently strong & well engineered to have withstood my stupidity; error, if you wanna be polite.
Is the chamber's dimension oversized toward the breech end? Could some earlier pits or corrosion have been removed from excessive honing? Just questions.
I have to ask myself if what we are looking at in this particular instance is not the result of an unsized hull minus the head from a previous round stuck in front of the fired round? That reads awkward at best. Said another way, if the previously fired reloaded round was previously fired in a substantively oversized chamber & not resized, could the metal head been ejected alone and the body of the hull become lodged directly in front of the fired round? Could it have been a loaded 20 w/the head still attached? Again, it is but another coupla questions.
