As Jimin Texas said, you will get 12 answers from 10 people :grin: but I would be looking at a ball size that was .010 to .015 under the bore size for a smoothbored pistol matched up with a fairly thin patch. In my opinion, with a smoothbore pistol, the sum of the ball diameter and twice the patch thickness should be equal to the bore size, or up to .010 larger.
If the pistol was rifled, I would lean towards using a thicker patch with a slightly smaller ball if I could find one. The sum of the ball diameter and twice the patch thickness should be equal to or .010 larger than the
groove diameter, the reason being, the patch must seal off the grooves in order to prevent excessive blow by and to be able to grip the sides of the rifleing so that it can impart the twists rotation to the ball.
Of course, this is just my opinion but, generally speaking I would use a .005 to .010 undersize ball with a .015 to .018 thick patch in a
rifle . I like the tight combination in a rifle.
A rifle is large, easy to grip, fairly heavy and is loaded with the butt plate resting on something. This allows using a tight ball/patch combination which will require quite a bit of force to start the ball into the barrel and to ram it down the bore.
With a muzzleloading pistol, it is difficult to hold it and start a very tight ball/patch combination like that into the bore. This is why I suggest a looser ball/patch combination for a pistol.
zonie