He has OVER 6thou of HS. This is a lot, and bullets aren't jammed, nor false shoulder, to stop the rounds from moving so forward on firing, from where they will stretch backwards to the boltface. Someone earlier mentioned lube in the chamber, and this could also be a bad combination if there.
On the positive side, he doesn't have such a HS issue with THAT brass anymore. And with proper sizing and rational loads he can make it last forever. He can develop loads with it now that it better matches his chamber. Would have been a waste of time to do so before this point anyway.
Barrel broke in,, good cartridge & components. Time to get down to business