Thanks for all the reply's, My main BP experience is with muzzle loading rifles, and I basicly if you can seat the ball against the charge your OK no matter how tight it was, I cant imagine the trouble it would be to seat a tight cannon ball in a badly fouled barrel, but on board ships at sea they must have done something to hold the balls in place against the charge, after all a vessel rolling from side to side would have had big trouble otherwise.
I plan on shooting lead balls or slugs and am considering making a mold to cast a hollow based bullet so the "skirt" can seal against the wall which are very smooth now they have been honed, compared to a muzzle loading rifle my cannon is "over built".
Thanks again guys, the info available here is mind boggling, you have to love the internet! I don't mind following rules if there is a reason,and I don't want to make anyone mad but all to often noone can tell you why, you just get told "It's the Rules"
~Monk~