Daryl, a patched round ball is always under bore diameter, but in a cartridge gun, I would think you would want something of at least groove diameter, to get proper engagement with the rifling. It is claimed that black powder will upset a slightly undersized lead ball or bullet upon firing, and cause it to fill the grooves. But I'd guess you would probably keep loads on the light side, considering the age of the gun, so very close to groove diameter would probably give the best accuracy.

Voting for anti-gun Democrats is dumber than giving treats to a dog that shits on a Persian Rug