.51 caliber roundballs.
I can also make minieballs for our 1850 style Enfield repro rifle.
I have a gun safe filled with single shot assault guns, and a few bayonets. Dates from the 1830s through the 1880s. Most of them real period pieces, not repros. We don't shoot those, but they do work. We also have about 6 shotguns and a couple of hunting rifles, and we have two flintlock rifles that are repros in styles from the late 1700s.
Only problem with black powder muzzleloaders is you have to be sure to clean them right away if you use them...
My father has a shotgun that is most likely an antique - we brought it to a gumsmith to get it fixed, the clip won't stayed closed - he said; "I can let you leave with this gun, the barrel is too worn" - my uncle had is gun at the same smith at the same time, the barrel on his gun was a lot more worn - but the gunsmith made no mention of that.
My father and uncle figured that it was an antique, and the gunsmith wanted to keep it!!