35 or 375 Whelen. Both have bullet options meant for slower cartridges, so you could easily load light recoil stuff or heavy hammers in the same gun. Either one is an easy rebore so you don't have to worry about dealing with contour changes in the stock, or sights if they have them, or bluing. If you'd rather rebarrel just keep in mind it'll cost a little more than most other actions with the coned breech and extractor cut.
