My only concern would be the choke. Many of the black powder shotguns unlike an actual smoothbore are choked. I am not sure if it would or could damamge the choke by shooting a patched round ball out of the barrel.

I have a Green Mountain .62 caliber smoothie (20 gauge) and after dropping a nitro card on the powder charge, I push down a .600 round ball with a thick cotton patch and have gotten some good accuracy out to 30 yards so far. I just got this barrel and have not had time to play with it a lot because I am working up a turkey load...