At a trade gun shoot in Oregon I shot balls made in an old Dixie (hair straightener) mold, and cut off with side cutters, and then let them roll around in a big old baking soda can in the back of my truck all the way from central California to Cooz Bay. I outshot guys I had been playing second fiddle to for years with those balls.
Chunk guns specifically built for those matches are often a lot more precision than the garden variety muzzleloader and might benefit from a coddled round ball, and then again maybe not.
Hungry Horse