I would buy a pound of 3f Goex and start with a powder charge of 50 grains. Shoot three times aiming at the same place on the target, swab the bore between shots with an cleaning patch that is barely dampened and not dripping with 91% rubbing alcohol. Do not adjust your sights or change anything at this point. After three shots then increase your load by 5 grains until your groups get nice and tight. Only after that do you adjust or file your sights, change shooting patch lubes, type of patch, diameter of ball, etc.
Swabbing the bore is just down and up, then either flip the patch over and do it again or just discard the patch, as you are just trying to return the bore to the same condition as the shot before it. Don't exceed more than 110 grains of 3f when using a PRB; less if and when you try a lead conical.