This Minié ball is a conical, cylindrical soft lead bullet with three grooves around the base of the cylinder. This type of bullet, used in muzzle loading rifles, became prominent during the United States Civil War.
Musket balls are an early form of ammunition, generally made from lead. The balls are muzzle-loaded into the barrel of a long gun, or musket, wrapped in a loosely-fitting paper patch and backed with gunpowder.