FN Five-seveN and GSh-18. Horizontal The FN P90 and Kel-Tec P50 personal defense weapons use horizontally mounted feeding systems. The magazine sits parallel to the barrel, fitting flush with the top of the receiver, and the ammunition is rotated 90 degrees by a spiral feed ramp before being chambered. The Heckler & Koch G11, an experimental assault rifle that implements caseless ammunition, also functions similarly with the magazine aligned horizontally over the barrel. Rather than being positioned laterally to the barrel like with the aforementioned examples, ammunition is positioned vertically with the bullet facing downward at a 90 degree angle relative to the barrel where it is fed into a rotary chamber before firing. The AR-57, also known as the AR Five-seven, is an upper receiver for the AR-15/M16 rifle lower receiver, firing FN 5.7×28mm rounds from standard FN P90 magazines. Casket Another form of box magazine, sometimes referred to as a "quad-column", can hold a large amount of ammunition. It is wider than a standard box magazine, but retains the same length. Casket magazines can be found on the Suomi KP/-31, Hafdasa C-4, Spectre M4, QCW-05 and on 5.45×39mm AK rifle derivatives. Magpul has been granted a patent for a STANAG-compatible casket magazine, and such a magazine was also debuted by SureFire in December 2010, and is now sold as the MAG5-60 and MAG5-100 high capacity magazine (HCM) in 60 and 100 round capacities, respectively, in 5.56mm for AR-15 compatible with M4/M16/AR-15 variants and other firearms that accept STANAG 4179 magazines. Izhmash has also developed a casket magazine for the AK-12. Rotary The rotary (or spool) magazine consists of a cylindrical sprocket actuated by a torsion spring, with cartridges fitting between the tooth bar of the sprocket, which is mounted on a spindle parallel to the bore axis and rotates each round sequentially into the feeding position. Rotary magazines may be fixed or detachable, and are usually of low capacity under ten rounds, depending on the caliber used. John Smith patented a rotary magazine in 1856. Another rotary magazine was produced by Sylvester Roper in 1866 and was also used in the weapons by Anton Spitalsky and the Savage Model 1892. Otto Schönauer first patented a spool magazine in 1886 and his later design, patented in 1900, was used on bolt-action rifles produced at least until 1979, among them Mannlicher–Schönauer adopted by the Greek Army in 1903. The M1941