The 5mm Remington Rimfire Magnum or 5mm RRM is a bottlenecked rimfire cartridge introduced by Remington Arms Company in 1969. Remington chambered it in a pair of bolt-action rifles, the Model 591 and Model 592, but the round never became very popular, and the rifles were discontinued in 1974. About 52,000 rifles and 30,000 barrels for the T/C Contender pistol were sold during its brief production run. Remington discontinued the cartridge itself in 1982, leaving owners with no source of ammunition.
In 2008, the cartridge was reintroduced by Mexico's Aguila Ammunition in collaboration with Centurion Ordnance.
Remington designed a completely new, bottlenecked case that was somewhat similar to the older .22 Winchester Magnum, but stronger to handle the higher pressure of the 5 mm at 33,000 PSI. It uses a 5mm (.204 caliber) bullet that measures 0.2045 inches (5.19 mm), the same as the more recent .204 Ruger center fire cartridge.
From 1982 until 2008, no ammunition manufacturers manufactured rounds for this cartridge. Some firearms manufacturers even created conversion kits to allow the existing 5 mm guns to shoot other more-common cartridges.
At the 2008 SHOT show, Aguila Ammunition announced they would reintroduce the cartridge and begin producing 5mm RMR ammunition in 2008. The cartridges are now available on the U.S. market branded as Centurion.
The 5 mm Mag offers higher velocity than the .22 WMR and more energy than either the .22 WMR or the later .17 HMR. It offers improved performance on small-game and for varmint hunting, along with excellent accuracy. The Aguila/Centurion 5mm Remington Magnum ammunition comes in two offerings: the original "White Box" with a 30gr dimpled jacketed soft point at 2300fps, as well as a Varmint "Yellow Box" round with a 30gr jacketed hollow point at 2400fps. Chronograph testing has shown that these rounds can actually run about 100fps faster than claimed by Aguila.
When Remington discontinued production of 5mm RRM ammunition, owners of Remington 591 and 592 rifles were left with excellent rifles but no ammunition for them. Mike Craig in 1994 in Seattle began work on a centerfire conversion of the 5mm RRM, the 5mm Craig. His company, Certech, also performed conversions of 5mm rifles from rimfire to centerfire by altering the bolt and installing a new firing pin, restoring them to use. Craig has since sold all the rights to the 5mm Craig to Eagle View Arms of Shelton, WA.
Original 591M and 592M rifles are still occasionally available on gun auction websites and at local gun shops and shows, prices running in the $500.00, plus or minus, range (2013).
For a brief time, Thompson Center Arms offered firearms in 5mm Mag.
At the 2008 SHOT show, Taurus International introduced the first handgun chambered for the 5mm Remington Magnum Rimfire. Concurrent with the announcement from Taurus, Aguila Ammunition announced they would begin producing 5mm RMR ammunition in 2008.
As of May 2011, Taurus has not yet imported nor produced their Tracker in 5mm RMR. They had stated that it will be manufactured and imported pending production demand in the second half of 2010.