It’s ironic that one of the best revolver cartridges is descended from an auto pistol. It’s also ironic that it’s one of the least known and least popular revolver cartridges. But that’s the way it is with the .45 Auto Rim (.45 AR). Even the cartridge development was backwards. Usually revolvers introduce new cartridges or and are redesigned for existing ones , in this case the revolver existed for 4 years before the cartridge was introduced.
This happened, because the in 1917, the United States declared war on the Central Powers. We were short of weapons of all types. We had the best combat handgun in the world, the Model 1911 .45 Automatic, but we did not have enough, nor could enough be made in time. Smith & Wesson chambered their large N frame revolver for the 45 ACP cartridge used in the Model 1911 pistol. Since the .45 ACP does not have a rim, it did not extract from double action swing out cylinder revolvers. A spring steel half moon clip was developed to hold the cartridges and engage the extractor. A collateral benefit was ease in loading or speed loading in combat situations. Both Colt and Smith & Wesson chambered their revolvers for the war effort and thousands served in the trenches with distinction.
After the war, a number of surplus Colt and Smith & Wesson Model 1917 were available, as well as post war production from Smith & Wesson. The .45 Auto rim cartridge was introduced in 1921 as a way to lead the revolvers with a conventional cartridge without the using the half moon clips. The .45 Auto Rim is exactly that a 45 ACP with a large thick rim. It can be hand loaded using .45 ACP data but it can handle 250 gr. bullets as well as full wad cutter designs.
Handguns chambered in .45 Auto Rim usually possess uncommon accuracy, easy to hand load, shoot well with cast bullets, have mild recoil. It may be unloved, but it’s a winner.