The British Brown Bess was 0.75 caliber, which is 3/4 inch. I think I recollect that it fired a 0.72 ball. The Charleville musket, I believe was 0.69 caliber, and would have fired an undersized ball, perhaps 0.66. 0.60 seems a bit small for a battle field drop, which I think your ball is. Doesn't look like it's been fired. In those days they didn't use a micrometer to size the bullet, the bore size was identified by weight, and a Brown Bess fired 12 balls to the pound. 0.69 caliber is about 16 balls to the pound. Your 0.60 find is very close to 20 balls per pound, and who knows for sure what size bores the Americans were using. The militia brought their own guns, so if you are on the battle field, it sure looks to me like you found a battle field drop by a militia soldier. After all, if you are in a fire fight, and are excitedly trying to load your muzzle loader and drop the ball, you going to bend over and pick it up? I really don't think so.
