Do your self a favor stay with rims. Almost any rimless cartridges ballistics can be duplicated in a rimmed case. I have had several single shots on the 38/55 basic case all extracted well. Right now I have a 30/40 which produces the same ballistics as a 308 in a strong single shot. That rifle is a switch barrel with a 2nd in 25 Krag that performs like a 257 Roberts.

No doubt if chambered in 308 and 257 I would have extractor problems.

Boats