Drum magazine

A drum magazine is a type of firearm magazine that is cylindrical in shape, similar to a drum. Instead of rounds being stored flat, as in a more common box magazine, rounds in a drum magazine are stored in a spiral around the center of the magazine, facing the direction of the barrel. Probably the first drum magazine to be patented was the one by Salloum Dahdah in 1862. A precursor to the drum magazine was the Accles drum, used for Gatling guns. The first true drum magazine was invented between 1908 and 1915 for the Farquhar-Hill Rifle, the patent for which can be found here.

There are several primary designs for a drum magazine. The most common is the cylinder type, that has a spider gear assembly that has an opening in each gear for two to three rounds of ammunition and can be loaded from the rear, used primarily in the AK-47. Another common design is the double-stack dual-horn drum, which operates like a standard stick magazine, but diverges the ammo into two separate feed chutes that run on a single cog. Rimmed ammunition including shotgun ammunition operated drums primarily run off a cogged (gear shaped) design which feeds each individual round of the ammo from the outermost edge of the drum. Recently a single-stack compact design has been released, which uses most of the interior capacity of the drum. It is driven by a single hub and telescopic shaft.

The advantage over traditional box-shaped magazines is that a drum magazine can carry much more ammunition, often two to three times that of a box magazine, such as the 71-round drum for the Russian PPSh-41 submachine gun, without making the gun too big to carry easily. Rear-loading drum magazines, such as the 75-round AK-pattern drums manufactured by Norinco, can be left loaded for extended periods of time without having any tension in the spring. The spring is then wound up when the weapon is ready to fire.

The downside to drum magazines is that they increase the overall weight of the weapon in which they are being used. They are also more prone to jamming due to the complex spring mechanisms they contain. Some drums also have a tendency to rattle when they are loaded with ammunition, possibly giving away the user's position.

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