.45 Auto Rim
|.45 Auto Rim|
On left: Two Remington UMC Auto Rim Factory Loads. On right: Two Peters Cartridge Auto Rim Factory Loads
|Place of origin||United States|
|Bullet diameter||0.452 in (11.5 mm)|
|Neck diameter||0.4685 in (11.90 mm)|
|Base diameter||0.4709 in (11.96 mm)|
|Rim diameter||0.5154 in (13.09 mm)|
|Rim thickness||0.0827 in (2.10 mm)|
|Case length||0.9004 in (22.87 mm)|
|Overall length||1.2646 in (32.12 mm)|
|Primer type||Boxer Large Pistol|
Two issues related to the use of .45 ACP ammunition in the M1917 revolver led to the development of the .45 Auto Rim. The M1917 had previously been used with half-moon clips that held three rounds of .45 ACP, a rimless cartridge. But if half-moon or moon clips are not used when firing a rimless cartridge in a revolver, the spent cases must be ejected by hand—either by shaking the revolver and its swing-out cylinder or by poking the cases with a rod or field-expedient tool, like a pencil—as the revolver's extractor cannot grab them. The second issue concerned headspace. In revolver cylinders not engineered to allow .45 ACP to headspace properly, as in early production Colt M1917s, the cartridges could slip forward, stopping them from firing. Adding a rim to the .45 ACP cartridge solved both these issues.
Loads offered were similar to the standard military loads for the .45ACP, but with fully lead bullets rather than the full metal jacket bullets used for .45ACP. This was done to reduce barrel wear in the shallow rifled revolvers in which it was to be used. The .45AR case is stronger than the .45ACP case and has a slightly larger case capacity, allowing for increases in performance. It can deliver similar performance to standard pressure loadings in older, dimensionally larger, revolver cartridge designs like .45 Colt.
The round is currently still in production by Corbon in their DPX and Performance Match lines of ammunition and is also manufactured by Georgia Arms and Buffalo Bore Ammunition.
- 45 Auto Rim - MUNICION.ORG
- Ayoob, Massad F. (2012). Massad Ayoob's Greatest Handguns of the World, Volume 2. Gun Digest Books. p. 41.
- Chuck Taylor, "The .45 Auto Rim", Guns Magazine (September 2000 ed.)
- Mike Venturino, "The .45 Colt sucks! Heresy? Listen-up before you blow a gasket!", American Handgunner (March–April 2005 ed.)
- ".45 AUTO RIM". Archived from the original on 2013-11-21. Retrieved 2013-11-18.