... i'd recommend first going the easy way with a .600" ball and a good greased .010" tight yarn cotton patch, then work up to .018".
actually, if the bore is truly .620", and the ball is truly .600", a .010" greased cotton patch will slide down the tube quite nicely with just a tad of effort, as it does for me and my chris walker smooth rifle. plus, do the math - .600" + .010" + .010" = .620", the bore size (we think). without any grooves to accept excess gathered patching, ramming home a ball patched with some materials much thicker than .010" could be, er, interesting ......
whence i attempted to patch with quality tight yarn .015" cotton patching it was a chore to get the ball down the barrel's throat let alone into its tummy. uh uh, loading and shooting shouldn't be a chore, sez me to me. bench fired accuracy at both 25 and 50 yards for both the .010" and .015" thick patching was the same, for me, with 60-75 grains of swiss 3f.
some local shooter friends have said that their tighter yet .018" patching worked just fine, but i wonder what effort it took to ram down such a configuration and was there any worthwhile added accuracy? as always, experimentation is required.
not often, but sometimes luck intervenes and i can hit the mark ...
