.45 Auto Rim

The .45 Auto Rim, also known as 11.5x23mmR, is a rimmed cartridge specifically designed to be fired in revolvers originally chambered for the .45 ACP cartridge.

.45 Auto Rim
On left: Two Remington UMC Auto Rim factory loads On right: Two Peters Cartridge Auto Rim factory loads
Type	Revolver
Place of origin	United States
Production history
Designed	1920
Manufacturer	Peters Cartridge Company Remington Corbon
Produced	1920–present
Specifications
Case type	Rimmed[1]
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	Large pistol
Maximum pressure (CIP)	17,400 psi (120 MPa)
Maximum CUP	15,000 CUP
Ballistic performance
Bullet mass/type Velocity Energy 160 gr (10 g) JHP 1,050 ft/s (320 m/s) 392 ft⋅lbf (531 J) 185 gr (12 g) LRN 800 ft/s (240 m/s) 264 ft⋅lbf (358 J) 230 gr (15 g) FMJ 855 ft/s (261 m/s) 375 ft⋅lbf (508 J) 230 gr (15 g) FMJ 750 ft/s (230 m/s) 287 ft⋅lbf (389 J)
Source(s): [2]

The Peters Cartridge Company developed the cartridge in 1920 for use in the M1917 revolver, large numbers of which had become available as surplus following the end of World War I.^[3]

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.^[2] 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.^[4]

.45 Auto Rim/.45 ACP cartridge

Loads offered were similar to the standard military loads for the .45 ACP, but with fully lead bullets rather than the full metal jacket bullets used for .45 ACP. This was done to reduce barrel wear in the shallow rifled revolvers in which it was to be used.^[5]

The round is currently still in production by Corbon in their DPX^[6] and Performance Match lines of ammunition and is also manufactured by Georgia Arms^[7] and Buffalo Bore Ammunition.^[8]

References

1. "45 Auto Rim - MUNICION.ORG". Archived from the original on 2017-02-09. Retrieved 2012-03-01.
2. Taylor, Chuck, "The .45 Auto Rim", Guns Magazine (September 2000 ed.), archived from the original on 29 October 2010
3. Ayoob, Massad F. (2012). Massad Ayoob's Greatest Handguns of the World, Volume 2. Gun Digest Books. p. 41.
4. Corbon
5. Mike Venturino, "The .45 Colt sucks! Heresy? Listen-up before you blow a gasket!", American Handgunner (March–April 2005 ed.)
6. "DPX Handgun". shopcorbon.com. Archived from the original on 28 October 2015. Retrieved 6 June 2022.
7. ".45 AUTO RIM". Archived from the original on 2013-11-21. Retrieved 2013-11-18.
8. ".45 Auto Rim Standard Pressure Pistol & Handgun Ammunition". www.buffalobore.com. Retrieved 2021-07-20.