The "roundball" rifles were generally "gauge" rifles, that is to say the bore size was designated by the gauge system like, 4,8,10,12 & 16 gauge rather than caliber in hundredths of an inch. Generally only the largest bores were fired with round balls, 10 gauge and smaller bores usually fired short conical bullets. I would assume, but do not "know", that bullets and balls were full groove diameter or slightly over, just like any other breech loading rifle.
