I'm with Mike Petrov; the .30-40 has all the power you'll need and also all the range. You can handload it from .32ACP power to .308WCF power in a strong rifle.

The only concern I'd have is the seasonal availability of loaded ammo; the manufacturers seem to make one "run" of .30-40 a year now. But if you handload, cases seem to be available all the time. And you have a WIDE choice of bullets! Plinkers, match grade, high sectional density/deep penetration, non-lead.....you name it, .308 has got it.