Goex, Swiss or Elephant Blackpowder. Use what you can find. Don't sacrifice and go with a substitute in a flintlock. 4F in the pan. 3F or 2F in the barrel. If 2F, 90 grains seems to work well with many folks. If 3F, 80 grains seems to be a good starting point.
If the barrel is 1/66, it is meant for round balls. If it is 1/48, rounds balls or 245 grain PBs will work well. The heavier and therefore longer PB and Maxi Balls don't stabilize well in slower twists. The Hornady Pa Conical is a great choice if you can find them.
My load is 90 grains of 2F behind a 245 grain PB Aerotip.
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