Non-expert thoughts.
Not caused by wrong case:
Cartridge obviously chambered - so not too long.
A short case would separate, but I'd expect the rear half would seal the chamber and why would the back of the case head blow off unless the locked bolt slipped back.
An over-size bullet would likely bulge or split the barrel.
Can these rifles fire out of battery? and if so, wouldn't the bolt have shot out the back?
Cracked receiver or extreme overcharge seems likely to me.
Last edited by night_owl; 12/28/20.
