The .22 Winchester Magnum Rimfire (5.6×27mmR), more commonly called .22 WMR, .22 Magnum, or simply .22 Mag, is a rimfire 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 1,750 feet per second (530 m/s) and 30 grains (1.9 g) at 2,250 feet per second (690 m/s). More recently, a high-quality 30gr Vmax cartridge from Hornady has been released. This exceeds 2200fps in a rifle and has a reputation for much greater consistency and accuracy than was previously attributed to this calibre. Accuracy around 1 MOA is achievable and this has led to this cartridge regaining ground previously lost to the excellent .17 HMR, especially as the 30gr bullet weight (nearly double that of the HMR's normal 17gr) gives it a reputation for hitting harder on larger varmints such as fox and coyote.
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 & 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/rifle. It was the only successful rimfire cartridge introduced in the 20th Century.
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 combination of more powder and higher sustained pressures gives velocities over 2,000 feet per second (610 m/s) from a rifle using a 30-grain (1.9 g) bullet, and 1,500 feet per second (460 m/s) from a handgun. A .22 WMR round will not fit into the chamber of a .22 LR firearm, but it is possible, though unsafe, to chamber .22 LR rounds in a .22 WMR firearm, although doing so can result in injury from gas leaking around the LR case which is undersized for a magnum chamber.
Since the .22 WMR generally uses the same weight bullets as the .22 Long Rifle, it is used in similar situations. The 40-grain (2.6 g) .22 WMR at 100 yards (91 m) 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-inch (76 mm) high target, the 40-grain (2.6 g) .22 WMR can reach ranges of nearly 125 yards (114 m). 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, or any varmint of 50 pounds or less at close range.
It first appeared in the Savage Model 24 combination rifle, followed by Winchester's own Model 61 pump-action rifle and Model 255 lever-action rifle. A number of single-shot and repeating rifles were offered in .22 WMR. 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 & Richardson produced the first American-made semi-automatic .22 WMR. In the 1990s semi-automatic .22 WMR rifles were also introduced by Ruger (10/22) and Marlin, and are currently produced by Remington (Model 597) and Tanfoglio Appeal Rifle as well as the Excel Arms Accelerator Rifle and Savage arms A22 magnum.
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.
The .22 WMR is an enlarged, more powerful version of the much earlier .22 WRF. Despite frequent claims to the contrary, it should not be used in any firearm except those specifically chambered for .22 WMR. Even firearms chambered for the .22 WRF are not suitable; for one thing, the case lengths are different, and the fact that the cartridge fits into the chamber does not guarantee that using the wrong cartridge is either safe or effective.
The .22 WMR was for a time the most powerful rimfire round available; it even outperformed the .22 WCF.
Though the .22 WMR is more powerful than the .22 Long Rifle, .22 WMR ammunition is not manufactured in as large a variety as .22 LR. It also is not as widely available in retail stores. Although .22 WMR ammunition is not necessarily hard to find, nearly every ammunition retailer stocks .22 LR, whereas many do not stock .22 WMR. Furthermore, .22 WMR is so much more expensive than almost all .22 LR that its price becomes a significant consideration where large volumes of ammunition are consumed.
Because many of the rifles that are chambered for the .22 WMR have tubular magazines, the bullet noses generally are flat or at least blunt to allow smooth feeding and reduce damage to the bullet. Although a pointed bullet in a rimfire cartridge will not contact the primer of the round in front of it (which is a hazard with centerfire cartridges in a tubular magazine), the manufacturer's stamp is in the middle of the base of a rimfire cartridge, and this may interfere with pointed metal bullets in a tube. However, Remington, CCI, and Hornady now produce bullet designs with 30 or 33-grain (2.1 g) polymer plastic ballistic tips that reduce the hazards of pointed ammunition in tubular magazines.
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).
The limited selection of commercial ammunition for the .22 WMR has inspired specialist wildcatters to select the .22 WMR case for handloading high performance rimfire ammunition. Generally they would load the wildcat cartridges with pointed bullets for the aerodynamic advantages, using the same bullets as those in .22 caliber centerfire cartridges. Though such bullets are generally heavier than standard .22 WMR bullets, the sharp nose and tapered tail conserve energy better, delivering greater impact at longer ranges.
Other wildcatters 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 such an experimental design is the Swedish 4.5×26mm MKR.