.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
Case type Rimmed[1]
Bullet diameter 0.452 in
Neck diameter 0.4685 in (Bad rounding hereScript error mm)
Base diameter 0.4709 in (Bad rounding hereScript error mm)
Rim diameter 0.5154 in (Bad rounding hereScript error mm)
Rim thickness 0.0827 in (Bad rounding hereScript error mm)
Case length 0.9004 in (Bad rounding hereScript error mm)
Overall length 1.2646 in (Bad rounding hereScript error mm)
Primer type Boxer Large Pistol
Ballistic performance
Bullet weight/type Velocity Energy
160 gr (Bad rounding hereScript error g) JHP1,050 ft/s (Bad rounding hereScript error m/s)392 ft·lbf (Bad rounding hereScript error J)
185 gr (Bad rounding hereScript error g) LRN800 ft/s (Bad rounding hereScript error m/s)264 ft·lbf (Bad rounding hereScript error J)
230 gr (Bad rounding hereScript error g) FMJ855 ft/s (Bad rounding hereScript error m/s)375 ft·lbf (Bad rounding hereScript error J)
230 gr (Bad rounding hereScript error g) FMJ750 ft/s (Bad rounding hereScript error m/s)287 ft·lbf (Bad rounding hereScript error J)

The .45 Auto Rim, a.k.a 11.5x23R is a rimmed cartridge specifically designed to be fired in revolvers originally chambered for the .45 ACP cartridge. Remington-Peters developed the cartridge for use in the M1917 revolver, large amounts of which had become available as surplus following the end of the Great War. The M1917 had previously been used with half-moon clips that held three rounds of the rimless .45ACP.[2] If half-moon or moon clips are not used with a rimless cartridge in a revolver, they must be ejected by hand with a rod or field-expedient tool like a pencil. In revolver cylinders not engineered to allow .45ACP to headspace properly, as in early production Colt M1917's, the cartridges could slip forward, stopping them from firing. Adding the rim solved both these issues.[3]

Loads offered were similar to the standard military loads for the .45ACP, but with fully lead bullets rather than the harder alloys 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.[2] It can deliver similar performance to standard pressure loadings in older, dimensionally larger, revolver cartridge designs like .45 Colt.[4]

The round is currently still in production by Corbon in their DPX[5] and Performance Match[6] lines of ammunition.


  2. 2.0 2.1 Chuck Taylor, "The .45 Auto Rim", Guns Magazine,
  4. Mike Venturino, "The .45 Colt sucks! Heresy? Listen-up before you blow a gasket!", American Handgunner,

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