Well, If it worked before with the SAME ammo prior I'd be looking at the extractor and/or ejector like Fred suggested. The bolt operation is the same with or without ammo. If the bolt functions normally without brass all thats left is the extractor, ejector, brass or the chamber, stuff forward the locking lugs. In fact you could reduce the parts to the bare minimum and odds are pretty good you would have the same condition. That is easily done , remove the firing pin ( place a piece of tape around the bolt body so the bolt head retaining pin doesn't fall out ) and both baffles. All you'll have together is the bolt body, handle and bolthead then chamber a round, preferably a dummy is at all possible.

If it were the bolt internals, ie; something restricting the cocking piece, the bolt wouldn't operate correctly either way, brass or no brass. If it were somehow the baffles, again, that would show up with or without brass.

Bill