The article titled casing is a disambiguation page.

A casing, also called the brass, is the part of a cartridge that contains the gunpowder charge, the primer, and the bullet. After a shot is fired, the casing is empty as its gunpowder charge has burned, as the primer has been used and as the bullet has been propelled. The empty case is often ejected automatically.

After a crime the police collects cases and bullets.