RE: .54 1/60" ball only??
nchawkeye has some good points (as usual). With the 1-60 twist it was basically designed for roundball. The .54 caliber roundball is about all the THUMP you will probably need when hunting. Also with the slow twist you can normally push the ball to the limit of the barrel and still get good accuracy. With just 100 grains of Pyrodex RS the ball will be 1729 fps which for a ball that size is moving.
I have a 1-66 .50 caliber I can shoot 100 grains of Goex 3f and the accuracy is excellent. I'd hate to guess how fast that ball is moving. It would have to be well over 1800 fps.
You might try some ball-ets, PA Conicals, and even some of the 300 grain REAL conicals and see how your rifle likes them. There is no guarantee that the rifle will shoot them fine, but it might as they are made somewhat like a ball design. The 310 ballet might shoot well out of there and give you almost 80 grains in weight.