What Is 22 Mag Ammo?   .22 Winchester Magnum Rimfire (WMR), commonly known as .22 Mag, was introduced by Winchester in 1959. Shortly after the release of new cartridges, Ruger, Savage, and Smith & Wesson built guns for the new caliber. These include revolvers or bolt-fired rifles, pumps, single-shot, and lever-action rifles.   .22 WMR is the answer for shooters wishing to have a...