.45 Auto Rim

The .45 Auto Rim is a rimmed centerfire cartridge that was developed in the early 20th century as an alternative to the .45 ACP cartridge. It was designed to be used in revolvers that could not reliably use the rimless .45 ACP cartridge, such as the Colt New Service and Smith & Wesson Model 1917.

The .45 Auto Rim has a bullet diameter of .452 inches (11.5 mm) and a case length of .898 inches (22.8 mm), which is the same as the .45 ACP cartridge. However, the .45 Auto Rim has a rimmed case, which allows it to be used in revolvers that require the use of moon clips to properly extract and eject the rimless .45 ACP cartridge.

The .45 Auto Rim is loaded to similar velocities and energies as the .45 ACP cartridge, with a typical muzzle velocity of around 800 to 900 feet per second (245 to 275 m/s) and a muzzle energy of around 350 to 450 foot-pounds (475 to 610 J). It is primarily used for target shooting and hunting, although it has largely been replaced by more modern cartridges in these applications.

While the .45 Auto Rim is not as widely used as some other handgun cartridges, it remains a popular choice among collectors and enthusiasts of classic revolvers. It also has some practical applications, particularly for shooters who prefer to use revolvers for self-defense or hunting and require the use of a rimmed cartridge.