Simply because of what you want to hunt... a .54 is the way to go. There are lots of conicals on line that will or should work in that Great Plain Hunter. The 1-32 twist will shoot most of the Great Plains Conicals real well and should shoot Lyman maxiball excellent. You can get them in bulk on line very reasonable.

Also like frontier gander said, you will never be under gunned. That .54 shoots a larger, heavier, more energy producing conical that will put a world of hurt on what ever you shoot.

Also you might want to get a new hot shot nipple for the Lyman when you order the rifle. The Lyman nipples sometimes give people problems for some reason. Good luck with your selection.

And Outdoorslover is right.. a .50 will also work, but I like big bores in traditional rifles....