You are not holding the rifle close enough to the computer to tell.
Couple of possibles- rough/dirty chamber is not allowing brass to release. Possible fix involves a drill, a .45 or 50 caliber brush, and some cleaning solvent. Remove bolt, chuck rod into drill, dip brush in solvent, insert into chamber, spin while moving in/out for 30 seconds, clean patch.
Other possible- nasty, nasty word- headspace. Is brass showing any signs of stretching about a 1/2 inch above the rim? If so, get thee to a gunsmith.