"It looks like an old shotgun shell "
A shotgun shell being discarded after firing a shotgun
Public DomainA shotgun shell being discarded after firing a shotgun - Credit: United States Government / Wikimedia Commons

A shotgun is a weapon that fires shot (small lead balls) or a slug (a heavy lead bullet). The shotgun shell is the cartridge that contains the shot or slug and the gunpowder and primer. When the gun is fired, the shot or slug is projected out of the cartridge, and the empty shotgun shell is discarded.