243winxb, I agree that a soft batch of brass would make the difference. But bass that soft is typically too soft for cartridge brass intended for commercial rounds that'll be reloaded. I'm surprised the factory let that stuff out the door.
Other causes with factory ammo case heads extruding back into bolt face cutouts are too tight a bore, extremely hot powder temperatures and just a plain bad lot of ammo.
US Navy Distinguished Marksman Badge 153
Former USA Palma Team Member
NRA High Power Long Range High Master
NRA Smallbore Prone Master