The .22 Winchester Magnum, more commonly called .22 WMR (for Winchester Magnum Rimfire) or .22 Magnum or simply .22 Mag, is a rimfire rifle cartridge. Commonly loaded with a 40 grain (2.6 g) bullet, it can deliver velocities in the 2000 ft/s range from a rifle barrel. It is also available with 30 grain loads (2 g) and can achieve speeds of 2300 ft/s.
The .22 WMR was introduced in 1959 by Winchester Repeating Arms Company, and 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's case is thicker, allowing higher pressures. The combination of more powder and higher pressures gives velocities over 2000 feet per second from a rifle using a 30 grain bullet, and 1500 feet per second (460 m/s) from a handgun.
Since the .22 WMR generally uses the same weight bullets as the .22 Long Rifle, it is generally used in similar situations. The 40 grain .22 WMR at 100 yards still retains the velocity of 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 high target, the 40 grain .22 WMR can reach ranges of nearly 125 yards. This makes the .22 WMR an effective short to medium range varmint rifle cartridge. The relatively quiet sound of firing and negligible recoil also make it a very pleasant rifle to shoot for extended periods of time. It is less expensive to shoot than its nearest competitiors, the centerfire.22 Hornet, the .17 HMR, and the new 5.7 x 28 mm.
The .22 WMR operates at pressures beyond what normal blowback actions typically handle, but in the 1990s semi-automatic .22 WMR rifles were introduced by Sturm, Ruger and Marlin Firearms. Also recently introduced is the new 597 model from Remington. Before this time, most .22 WMR firearms were bolt action rifles, though the .22 WMR is also found in a number of revolvers by Taurus, North American Arms, Tanfoglio, and Sturm, Ruger, and was previously available in semi-automatic pistols by the now defunct manufacturers AMT and Grendel (the AMT has since been resurrected by High Standard). Both of these designs used specially designed chambers with flutes or gas ports, designed to lubricate the long, thin cartridge with gasses from the chamber, overcoming the Blish effect and allowing easy extraction of the cartridge.
While the .22 WMR is a more powerful cartridge than the .22 Long Rifle, ammunition is not available in as large a variety as .22 LR ammunition. Availability is also not as great as the .22 LR; 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 ammunition, though it is less expensive than ammunition in 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 grain poly-tipped ballistic tips called the V-Max, all produced by Hornady. While a pointed bullet is not going to rest against the primer of the round in front of it (like 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.
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 these bullets were 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 (see external ballistics).
The .22 WMR was also the basis for the first new commercial rimfire of the 21st century, the .17 HMR. The .17 HMR, with its tiny .172 caliber (4.5 mm) bullet, offers much higher velocities and a flatter trajectory than the .22 WMR, though the .22 WMR still offers better penetration with its heavier bullet (see terminal ballistics).