With a .680 round ball, I wouldn't use much more than a .010 wonderlubed patch. I shoot Pedersoli's 1777 Charleville and Springfield 1816 with a .678 round ball, .010 patch and 80 gr FFg... once I figured out where to hold, both will put all the rounds in the center of the chest of a Transtar 2 target at 50 yards. I have .680, .678 and .662 round ball and various thickness of patches, and you might want to experiment to see what combination your musket likes. Wonderlube/Bore Butter type products do a superb job keeping the fouling soft.