Beta C-Mag

The Beta C-Mag is a 100-round capacity drum magazine manufactured by the Beta Company. It was designed by Jim Sullivan and first patented in 1987 and has been adapted for use in numerous firearms firing the 5.56×45mm NATO, 7.62×51mm NATO, and 9×19mm Parabellum cartridges.^[1] C-Mag is short for century magazine (The letter C is also the Roman numeral for the number 100), referring to its 100-round capacity. It has two drum units, each of which hold half of the cartridges inserted into the magazine. The latest version of the magazine is available with a transparent backing to allow the user to see the number of rounds remaining in the magazine.^[2] A C-Mag loaded with 5.56×45mm NATO ammunition typically weighs about 2.1 kg (4.63 lb); a C-Mag loaded with 7.62×51mm NATO ammunition weighs 4.77 kg (10.5 lb).

A version adapted for the M16 rifle is used by the U.S. military. The magazine design, including drawings, is covered in detail in U.S. patent 4,658,700.