Is it a flintlock or percussion? If its a flintlock, I would only use Black Powder. (FFg for .50 cal or FFFg if .45 cal). Percussion, you can use black powder or as a substitute I would recommend Pyrodex RS or P. As for a projectile you can try patched round balls, Maxiballs, or T/C Shockwaves in 250 or 300 gr. Powerbelts either have a good following or are hated for lack of performance on game.