Could also have been a huge over pressure from bullet set back - I've seen some .40 JHP that my co-workers keep chambering, clearing, and rechambering that have MAJOR set back.
Cleaning the range the other day I found a .40 with the bullet set about halfway back in the case (far enough that there was air between the case mouth and the bullet). And: a (lightish) primer strike. A kb but for the grace of god.
Way too many shooters, so no idea whose it was but eeeesh!
Doesn't anyone check their chambering count? I fine-tip sharpie the back of the top round in the mag before loading. Line is fine, X = bottom of mag. When I get about 10 in my carry loads, I famfire the whole thing and load fresh ammo across the board. This weekend, 4th fun shoot when everyone was loading up their ECD guns at the end of the day the 'best' anyone else did was "gently load."