Oh yeah - 24 bore - .58 about - (actual .579"). Leatherbelly shoots a full 80gr. of 2F in his 'tight' 28 bore smoothie, which is .54 cal. A true 28 is .55", a 29 is .544" and a 30 is .538". Note, he shoots a 34 bore ball.(.516", or thereabouts)
currently, I am using 3 drams in my Enfield Musketoon (Confederate version), which is between 25 and 24 bore as it's a .574" bore. I started off working up to 75gr. which shot quite well and gave me 1,308fps, considerably higher than Lyman got back in the 70's in their 24" bl. I lost my 75gr. measure but had a lot of 3 drams measures (82gr.) so tried that and it shot even better - as expected. Experience is a wonderful teacher in this stuff. Light recoil, about 1,350fps and 3" at 100 meters, which I figure is OK due to the battle sights, short bl. and sight radius and my old eyeballs- besides, it's a rifle.
So - there ya have it. Actually, the further you get the ball out there before it takes on a spin and becomes a curve ball, the better accuracy range you will have at ranges past 25 yards. LB is a really good shot, with that 24 bore. I should buy it from him!