A firearm cartridge is composed of four parts: the case, the gunpowder, the primer, and the projectile. The case is the shell containing the powder, and the primer is an small amount of explosive tightly packed in a small brass casing or blister at the base of the cartridge case, at the other end of which there is the projectile, which is commonly called bullet by civilians. How does a cartridge work? Once in the rifle breech, the cartridge primer is struck by the bolt firing pin; as it ignites it detonates the powder contained in the case. The extremely high-pressured ignition hot gases propels the projectile off the cartridge case, through the rifle barrel and out of its muzzle at high speed, which is called muzzle velocity. If the barrel is rifled (contains spinning grooves), the projectile will spin through the air, travelling with greater accuracy.