You can use FFg or FFFg and these cartridges were meant for black powder. Find out where the base of the bullet sits in the case and fill the case to that height, plus 1/10" (or so). Black powder likes to be compressed a bit. I shoot 35 gr. FFFg GOEX with a 250 gr. bullet. Your maximum loads will also be your most accurate loads, and will most likely shoot to the sights, where lesser loads will not. Black Powder pressures are low, so there is no danger factor here, assuming your barrel will accommodate .452" .45 cal bullets.