Yes ball will be hard to come by. Warrens used to make ball of all sizes, but they kind of stopped that I think. Lee Molds are your best bet. A .550 would be about right. That would give you room for a patch. In my .62 caliber smoothbore I shoot a .600 and a .610 ball. Sometimes with a patch, sometimes without. Mine is not accurate to 100 yards, no matter what I have tried. Although that depends on what you call accurate. 40 yards is about max with the smoothbore, but I'd hate to have that 324 grain ball smack me..