Seems to me, the calibre of ball in the issue ctgs. was in the .69 to .70 range.
With the normal British Musket of the day being the Bess, in one or more of it's varieties being .75 to .80 cal, you can see one reason for the atrocious inaccuracy. Yes - being smooth didn't help, however with less windage between the ball and bores, accuracy was improved immensely.

The US military muskets up to and including the 1842 model in caplock, were of .69 cal. (.690 to .700") and those ctg.s used balls of .64" cal until 1820 when their calibre was increased to .65". This virtually doubled the hits at 100 yards, which was still dismal,ie: 2 to 4 on a 3' target at 100yards out of 10 shots is still better than 1 or 2.

Due to the inaccuracy of a single 'shot' in the ctg., buck and ball ctgs. were much more popular as they quadrupled the wounding factor. This, of course was due to the inclusion of 3, 000 buck with the round ball loading.

Buck and ball loads are a LOT of fun in a pistol, Curl! I do understand some reluctance to shoot these beautiful pistols very much - however, to touch off a few shots from each, would indeed make them happy. A squib load of about 40gr. 2F should work just fine.

With bores that large, you can shine and even drop a small diameter flashlight down the bores to inspect the interiors from the muzzle end.