Bullet found loose in military objects box. Example of a Civil War era "Minie Ball" used in rifled muskets by both sides during the war. A common type of bullet used in mid 19th c warfare. Conical bullet in 0.58 caliber, three grooves for lubricant near the base of the bullet. Concave depression on the underside of the bullet, allows for gases from powder charge to expand the thin walls of concave cavity to grip rifling. Not oxidized - covered in a protective coating? Inert, no powder or explosive (used in muzzleloading rifle, with separate black powder charge).