I tried patched round balls in my 1:28" twist 50 cal in-line, but never got good groups, not even with light powder charges.
My plinking load, also used occasionally to dispatch nuisance critters, is a hard cast SWC 240gr .430 bullet in a green Hornady sabot on top of 40 gr of Pyrodex RS. It's accurate in my rifle, mild recoil, and more than enough for small game.
Marc