RE: .338-06 Ackley
I don't think you could go wrong with this choice. It probably comes closer to an "all-round" caliber for North American and African plains game than any other!! I believe it will feed from the magazine with no modifications. You could probably get a dummy round or two from someone to try for feeding before you rebarrel. I know a plain .338/'06 would feed from a .270 mag. with no alterations. This round, with the correct bullet, would be excellent for ANY North American game shooting!!
Keep yore powder dry!!