High Quality Content by WIKIPEDIA articles! The .22 Winchester Magnum Rimfire, more commonly called .22 WMR, .22 Magnum, or simply .22 Mag, is a rimfire rifle cartridge. Originally loaded with a bullet weight of 40 grains (2.6 g) delivering velocities in the 2,000 feet per second (610 m/s) range from a rifle barrel, .22 WMR has also been loaded with bullet weights of 50 grains (3.2 g) at 1,530 feet per second (470 m/s) and 30 grains (1.9 g) at 2,200 feet per second (670 m/s).