A metal container for holding cartridges for rapid reloading. It differs from a clip in that it also contains a means for advancing the cartridges. A common design is a rectangular “box” magazine with cartridges stacked in a single column or a staggered double column with a spring underneath them. After a cartridge is fired and the case extracted, the spring (“follower”) pushes the next cartridge up to be stripped off by the advancing bolt and pushed into the chamber.
Larger magazines take the shape of drums containing cartridges lined up in concentric layers under spring pressure. Magazines are differentiated as external (detachable) and internal where they are fixed to the receiver of the gun. Detachable magazines can be much larger and permit much faster reloading, and they are one of the evil features defining assault rifles under the AWB. This feature is generally considered the most important of the six and subject to the most scrutiny.