I used .311" from a DC Lee Mould, as well as .320" from a .319" Lee DC mould. I tried using Hornady buckshot of .320", but they were too hard and difficult to load.
With pure lead, even the .320" were easy to load with .0225 patches (10oz. denim). I didn't even need a short starter- just put the .320" ball on top of the patch, choke up on the rod and push them into the bore. The ball and patch would easily conform to the bore, even though the ball was already bore size. No matter what patch and ball I used (all snug) this rifle never needed wiping while shooting. each time you load, you clean the last shot's fouling. There is NEVER any buildup inside the bore - only a minor amount in the breech, that the patched ball never sees.