I've always used .520"s in my .54cal smoothbores...started with Hornady's, then coordinated an order big enough for Eddie May in Chatsworth, GA to buy a mold and add the .520" to his inventory of cast balls.
42" Rice barrel, 90rns Goex 3F, .022" Oxyoke patch, .520" balls...shoots almost like a rifle at 50yds.
Track sells their Hornady .520"s for $18.00 / 100...I bought 1000 from Eddie May for $8.70 / 100...less than half of TOW's price.