YOu will get more complete ignition of the FFg Goex powder if you us a OP wad, or filler under that PRB. Also, Using as tight a ball and patch combination improves accuracy. Try the .495, and even the .500 diameter balls to see if you get better accuracy. Wiht the OP wads or fillers, you may find you can reduce the amount of powder used and still get the same velocity, but less recoil.
When Hunting, use that tight ball for your first shot, when you have the time to load it properly before you leave camp or car. Carry the .490 balls and patching for reloads, ( in a ball block?) if needed, in the field. They are certainly accurate enough for a follow up, or Coup d'Grace shot on a downed deer.
Good hunting.
Sorry, I can't help you with a load for your .54, but you can use these same principles in establishing such a load for your gun. Many shooters here have recommended 70-90 grains of FFg or FFFg powder. Use what you barrel shoots the best for you. Start with the .530 ball, and then try the .535, or even a .540 ball in the gun to see if that doesn't improve your groups.