I just chambered and closed the breech on an old 2 3/4" 12 ga. roll crimped shell. As I said my chambers are long at 2 5/8". It's very old but I think it is loaded with smokeless powder. To fire this shell would be very dangerous, but I had no trouble closing the breech. But, a 2 3/4" shell is a 2 3/4" shell no matter what it"s loaded with. A roll crimped shell is of course longer than a folded crimped shell in the unfired condition. Once they are fired they will be the same length. The have to be; otherwise they are not 2 3/4" shells.