I'm guessing you will be using real blackpowder..... Goex perhaps.

Another couple options for bullets in that assumed 48-twist are these below. I suggest similar to Cayugad, but a couple drops lower.... like 70 grains for a starting point. Work up in 10-grain increments until good accuracy is achieved. Then perhaps tweak it, going either 5 grains up or five grains down.

http://www.hornady.com/store/50-Cal-240-gr-PA-Conical/
240 grains

http://www.cabelas.com/product/Thomp...all/740550.uts
320 grains