.22 Winchester Magnum Rimfire
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The .22 Winchester Magnum Rimfire, also known as the .22 WMR, .22 Magnum, .22 WMRF, .22 MRF, or .22 Mag, is a rimfire cartridge. Wikipedia
Pressure: 24,000 psi
Bullet diameter: .2285 in (5.804 mm)
Designed: 1959
Manufacturer: Winchester
Parent case: .22 WRF
Produced: 1959–present