1:70 twist sounds like Forsythe rifling, meant for propelling round balls with heavy charges. The problem is that no matter how fast they start out, 50 caliber round balls only retain about half their muzzle energy at 100 yds. Just too much air resistance, especially when launched at sonic speeds. A conical will retain energy much better down range, but starts slower and with a heavy charge may develop too much pressure and recoil for accurate shooting. Unless there is a need to shoot beyond 100 yds at deer size game or larger, I'd stick with the round balls.