I am shooting two .54s, one with a Getz barrel and the other with a Rice barrel. The Rice barrel requires more powder to get in the bull accurately, but I am not sure how that applies to your make barrel. Each is a little different. But a good starting point would be IMHO ~ 80 gr fffg or 90 gr ffg. Work up from there. Saturday I finally shot a good group dead center with my 44" swamped, Rice-barreled .54 rifle at 50 yds using .015 patch, .430 ball and 85 gr fffg GOEX. {my problem has been old age eyesight--I can either see the target clear or the sights clear, but not both at the same time!} This particular rifle is one I reported on some time ago that was shooting low--part of the problem was remedied by filing off most of the front sight and the other part was just me dropping the muzzle slightly at the trigger pull--I corrected that and the groups finally got in center! The eyesight part I partially solved by taking off my prescription glasses [and wearing clear safety glasses] so I could focus on the sight picture, then using a high contrast target I could see, if fuzzy, without corrective lenses. The light was just right, which makes me suspicious that I couldn't repeat the shots in a hunting situation...