Not only is the .45 Auto Rim cartridge rimmed, but it has a doubly thick rim, intended to take up the space occupied by the rim and the moon clip. This allows the .45 Auto Rim to be used in revolvers like the Mode 1917 S&W and the Model 1917 Colt revolvers. It cannot be used, without alteration, in either an auto loading pistol chambered for the .45 ACP or in a revolver with conventional headspace. The .45 Auto Rim can, however, be adapted to revolvers chambered for the .455 Webley by trimming the rim down from the front, thus thinning it to fit in revolvers chambered for the .455 revolver round. With some extra work, it can be made to work in pistols chambered for the .455 Webley Auto Pistol cartridge by thinning the rim, cutting an extractor groove, and trimming the rim to a semi-rim.
Jim