I really don't want to claim allegiance to any particular hypothesis for the gun in question, but aren't all blown guns the product of "over pressure"? At least, relative to what that particular gun can hold, that is, in fact, absolutely the case.
the anomalies with the case simply shows what happens when an a case becomes unsupported (because half the chamber disappeared). So I don't think it is really possible to convict the reload of overcharging.
Just 2 cents from the sidelines.
Brent, I take "over pressure" as referring to more pressure than the gun was built to handle. Gun passes proof, which is extreme over pressure . . . but fails somewhere in the future. Maybe the result of metal fatigue or a flaw that the proof load didn't reveal. For example, I know of one case in which a modern Spanish gun (reputable maker) failed, fired with a factory load. Several inches forward of the chamber. No indication of an obstruction. Examination revealed that barrel wall thickness where it blew was something like .014. Yet it had been shot for a long time before the thin spot blew. Unless we assume an overpressure factory load, that failure was the result of a flaw in the barrel boring process, which left the thin spot in question. Hard to tell why it blew then rather than sooner, or how it managed to survive a proof load.
