FYI, there's and old saying for shot loads in ML smoothbores:
"Load powder, more lead, shoots far, kills dead"
I use that approach in my smoothbores and here are 25 yard examples of 60grns Goex and 100grn shot charges of 5's or 6's, and 90grns of 7.5's out of my 42" barreled .54cal smoothbore...