Steve, it's been a few years since I examined a 30-30 54, but I think the factory put a spacer into the normal '06/.270 mag box to adapt it to .30-30. Same as adapting the 70 to such cartridges as .220 Swift. But may also have needed a slant insert to keep the rims from tangling. Maybe one of us has a 54 30-30 and can take a look.