.45 Auto Rim (using Hornady bullets)
Date: Mar 25 2016
The .45 Auto Rim was introduced by Peters Cartridge Company around 1920, allowing shooters to use a rimmed cartridge for easy extraction in the Smith & Wesson and Colt US Model 1917 revolvers, as well as their commercial counterparts. This effectively eliminated the need for half- and full-moon clips used in conjunction with .45 ACP cartridges, which were slow at best to load and unload, and often required the aid of some form of tool.
There are no major ammunition factories currently offering factory loads; however, there has been renewed interest and Starline offers brass (available factory direct at 800-280-6660), and several smaller companies such as Black Hills, Buffalo Bore, etc. offer factory loads.
Smith & Wesson continues to offer revolvers chambered in .45 ACP with correct headspace to accept the .45 Auto Rim cartridge. However, many modern Ruger, Colt, Uberti and USFA .45 Colt single-action revolvers fitted with an extra .45 ACP cylinder do not headspace correctly to accept the .45 Auto Rim cartridge. A qualified gunsmith can correct headspace in just a few minutes by removing steel from the breech of the cylinder to accept .45 Auto Rim but still allow the use of .45 ACP ammunition.
Unlike the .45 ACP, the .45 Auto Rim headspaces on the rim, allowing a standard roll crimp when using bullets with a crimp groove or cannelure. However, neither of the Hornady bullets in the accompanying data feature a cannelure. Therefore a standard taper crimp die was used, with the case mouth being crimped to .470 inch diameter. This will not damage bullets, but still offers enough bullet pull to keep them solidly in place and aid with powder ignition. It is suggested to seat bullets to their correct overall length prior to applying the crimp.