.222 Remington Magnum
|.222 Remington Magnum|
|Place of origin||USA|
|Parent case||.222 Remington|
|Bullet diameter||.224 in (5.7 mm)|
|Neck diameter||.253 in (6.4 mm)|
|Shoulder diameter||.357 in (9.1 mm)|
|Base diameter||.376 in (9.6 mm)|
|Rim diameter||.378 in (9.6 mm)|
|Case length||1.850 in (47.0 mm)|
|Overall length||2.280 in (57.9 mm)|
|Primer type||Small rifle|
|Maximum CUP||50,000  CUP|
|Test barrel length: 24"
Source(s): Hodgdon 
The .222 Remington Magnum was a short-lived commercially produced cartridge derived from the .222 Remington. Originally developed for a US military prototype Armalite AR-15 rifle in 1958, the cartridge was not adopted by the military, but was introduced commercially in sporting rifles.
The .222 Remington Magnum was created by lengthening the case and shortening the neck of the highly accurate and very popular .222 Remington cartridge, which dominated varmint and benchrest shooting during the 1950s. Case capacity is about 20% greater than that of the .222 Remington, producing moderately higher muzzle velocities. The .222 Remington Magnum served as the basis for the German-developed 5.6×50mm Magnum sporting cartridge.
It was not until 1963 that the Army adopted a .22 caliber (5.56mm) assault rifle and cartridge, the M16 rifle and the 5.56×45mm NATO cartridge. The .223 Remington, the commercial variant of the new 5.56×45mm, was introduced a month before the official adoption of the military cartridge. The .223 Remington has a shorter neck and the shoulder is moved back slightly compared to the .222 Magnum. Case capacity is about 5% smaller than that of the .222 Magnum, but it was loaded to a slightly higher pressure, so the ballistic differences are almost nonexistent. As any widely used military cartridge is guaranteed to be a success on the commercial market, the .223 sold exceptionally well and the .222 Magnum faded rather quickly. Remington continued to offer the .222 Magnum in a couple of target and varmint rifle models for many years, but currently (2007) there are no commercial manufacturers either of rifles or ammunition in .222 Magnum other than Cooper Firearms of Montana. The .223 cartridge will fit in a .222 Magnum chamber, but due to excessive headspace the case is likely to rupture on firing.
The .222 Magnum has not entirely gone, however. It lives on in the hands of handloaders and the original cartridge became the parent round for a new development introduced in 2004, the .204 Ruger. The .204 Ruger is based on the .222 Magnum case necked down to hold a .20 caliber (5 mm) bullet.
- ".222 Remington Magnum" (PDF). Accurate Powder. Western Powders Inc. Retrieved 21 September 2010.
- Hodgdon Online Reloading Data
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- .222 Remington and .222 Rem Mag at Chuck Hawks