The .22 Winchester Magnum Rimfire, also called .22 WMR, .22 Magnum, .22 WMRF, .22 MRF, or .22 Mag, is a rimfire cartridge. Originally loaded with a bullet weight of delivering velocities in the range from a rifle barrel, .22 WMR is now loaded with bullet weights ranging from at to at . History The .22 WMR was introduced in 1959 by Winchester, but was not used by Winchester until the Winchester Model 61 slide rifle could be chambered for it in 1960. The first rifle to be offered in the new chambering was the Marlin Levermatic rifle in 1959, because its design was easily modified to accept the more powerful cartridge. By the time of the introduction of the Winchester 61, Smith & Wesson and Ruger had revolvers for it, and Savage had come out with the Model 24 and since late 2012, the Model 42, a more modern update than the 24, a .22/.410 rifle/shotgun combination gun. It was the only successful rimfire cartridge introduced in the 20th century. Dimensions and loading The .22 WMR uses a larger case than the more popular .22 Long Rifle (LR) both in diameter and length. The .22 WMR case is a lengthened version of the older .22 WRF and both of these cartridges have the bullet seated within the case, instead of using a heeled bullet as in the .22 LR. In the most common modern .22 WMR loadings using a bullet, the combination of more powder and higher sustained pressures gives velocities of from a rifle and from a handgun. A .22 WMR round will not fit into the chamber of a .22 LR firearm due to the greater length and width of the magnum case. Although the bullet diameters are the same, the larger .22 WMR chamber does not support the smaller .22 LR cartridge. Firing the smaller .22 LR round in a .22 WMR chamber results in swollen or split cartridge cases, high-pressure gas leakage from the rear of the chamber, and bullets striking the chamber throat out of alignment, which can result in injury to the shooter or bystander and which does result in poor ammunition performance. Gun makers offer .22 revolver models with cylinders chambered either in .22 LR or in .22 WMR and as convertible kits with both cylinders which allow the shooter to easily switch calibers on the same firearm. Uses Since the .22 WMR