What was slightly brilliant about some of Bull's designs of shells for some of his large calibre guns was the thick outer protective sheathing which was fired with the shell. This then parted company shell shortly after it left the muzzle and then dropped away. This meant that the diameter of the shell was significantly smaller than the bore of the gun but also allowed for the provision of stabilising fins to be incorporated into the design of the shell. I would guess that these fins would more than compensate for the lack of a rifled barrel.