.22 Winchester Magnum Rimfire

The .22 Winchester Magnum Rimfire, more commonly called .22 WMR, .22 Magnum, or simply .22 Mag, is a rimfire cartridge. Originally loaded with a bullet weight of 40 gr delivering velocities in the 2000 ft/s range from a rifle barrel, .22 WMR has also been loaded with bullet weights of 50 gr at 1530 ft/s and 30 gr at 2200 ft/s.

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. By that time, Smith and 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 revolver. It was the only successful rimfire cartridge introduced in the 20th Century.

Dimensions & Loading
The .22 WMR uses a larger case than the more popular .22 Long Rifle, both in diameter and length. The .22 WMR case is a lengthened version of the older .22 WRF. The .22 WMR's case is thicker than that of the .22 LR, allowing higher pressures. The combination of more powder and higher pressures gives velocities over 2000 ft/s from a rifle using a 30 gr bullet, and 1500 ft/s from a handgun. A .22 WMR round will not fit into the chamber of a .22 LR firearm but is possible to chamber .22 LR rounds in a .22 WMR firearm. This is potentially hazardous due to the difference in case diameter. When fired, the .22 LR case expands in the chamber, which can cause the case to split open or become stuck. Also, the long rifle bullet will travel in the magnum chamber unsupported for 0.4" before entering the barrel causing leading in the chamber.

Uses
Since the .22 WMR generally uses the same weight bullets as the .22 Long Rifle, it is used in similar situations. The 40 gr .22 WMR at 100 yard still retains the same velocity as a .22 LR at the muzzle, which can provide improved penetration at all ranges and more reliable expansion at longer ranges with expanding bullets.

If sighted in for maximum point blank range on a 3 in high target, the 40 gr .22 WMR can reach ranges of nearly 125 yard. This makes the .22 WMR an effective short to medium range varmint rifle cartridge. The relatively quiet report and negligible recoil also make it a very pleasant round to shoot for extended periods. The .22 WMR can take down small game such as rabbits, groundhogs, prairie dogs, foxes, racoons, and even coyotes at close range.

Firearms using .22 WMR
It first appeared in the Savage Model 24 combination rifle, followed by Winchester's own Model 61 pump action rifle. A number of single-shots and repeaters were offered in .22WMR. The .22 WMR operates at pressures beyond what normal blowback actions typically handle, but the self-loading Jefferson Model 159 was introduced for the cartridge. Until the 1990s, most .22 WMR firearms were bolt action rifles. In 1977-1985 Harrington and Richardson made the first American-made semi-automatic .22 WMR. In the 1990s semi-automatic .22 WMR rifles were also introduced by Sturm Ruger and Marlin, and are currently produced by Remington and Tanfoglio as well as the Excel Arms Accelerator Rilfe.

Revolvers in .22 WMR are made by Smith & Wesson, Taurus, North American Arms, Heritage Arms, and Sturm Ruger. Semi-automatic pistols for this cartridge are (or were) produced by Kel-Tec, Grendel and AMT, the latter two now defunct (AMT has been since resurrected by High Standard). The Grendel, AMT and Kel-Tec designs used specially designed chambers with flutes or gas ports, designed to lubricate the long, thin cartridge with gases from the chamber, overcoming the Blish effect and allowing easy extraction of the cartridge. High-Standard produced various models and versions of their classic two-shot over/under derringer in both .22 WMR and .22 LR.

The Argentine EDDA submachine gun uses the .22 WMR round.

Ammunition
The .22WMR is an enlarged, more powerful version of the much earlier .22 WRF, which is not, as commonly stated, usable in any firearm chambered for any other round, including .22WMR. The case lengths are different, and "just because it fits" is not a good reason to do it. It was for a time the most powerful rimfire round available, and even outperformed the .22 WCF.

While more powerful than the .22 Long Rifle, ammunition is not available in as large a variety as .22 LR. Availability is also not as great, either; while the .22 WMR is by no means hard to find, nearly every retailer that sells ammunition will carry .22 LR. The price of .22 WMR is substantially higher than almost all .22 LR, though it is less expensive than the new .17 Rimfire calibers. Since many of the rifles that chamber the .22 WMR use tubular magazines, bullet noses are generally flat or blunt to allow smooth feeding. Recently, new bullets have emerged from Remington, CCI, and Hornady and have 30 or 33 gr polymer plastic ballistic tips. While a pointed bullet is not going to rest against the primer of the round in front of it (as in a centerfire cartridge), a pointed bullet could still hang on the manufacturer's stamp, which is found in the middle of the base of the cartridge.

Bullets for the .22 WMR are generally unlubricated lead with heavy copper plating, in either solid nose or hollow point style designed for small game hunting or pest control (varmint hunting).

Due to the limited selection of commercial ammunition, the .22 WMR was the case used by a small but dedicated group of wildcatters for handloading high performance rimfire ammunition. Generally these loads would use more aerodynamic pointed bullets, the same type used by .22 caliber centerfire cartridges. While often heavier than standard .22 WMR bullets, the sharp nose and tapered tail retained velocity better, and delivered more energy downrange. Other wildcatters would neck the .22 WMR down to smaller calibers, such as .20 (5 mm) and .17 (4.5 mm) or even smaller, in an attempt to get maximum velocity and the flattest possible trajectory. An example of which is the Swedish studied 4.5×26mm MKR.

Applications
The .22 WMR is effective out to 125 yd (115 m) on varmints such as fox or coyote. When loaded with hollow-point bullets, it is too destructive for small game (under 50 yd [45 m]), such as rabbits or prairie dogs or anything intended for eating.