For those who have been following this thread, there is an article of interest in the current issue of "Handloader" magazine by Terry Wieland entitled - "Forensic Ballistics & Unsolvable Puzzles".
He mentions a couple cases where forensic analysis was unable to determine the cause. In one case, it was a Ruger #1 in .308 that blew up after 14 rds of the same ammo were fired. The powder used made it impossible to double charge without overflow. Even if a heavier bullet had been inadvertently loaded, the powder charge was within safety parameters.
In another, a .270 rd that had an enlarged primer pocket after half a dozen shots with the same ammo. The powder was a slow burning type that filled the case to capacity. All remaining bullets and ammo were checked for consistency.
In both cases, charges were weighed after being thrown by a powder measure. He is still baffled by the incidents.