Under the metric cartridge designation system, a capitalized "R" added at the end of the designation denotes a rimmed cartridge. For example, "7.62×54mmR" is a rimmed cartridge, while "7.62×51mm" is a rimless cartridge. Under Imperial designations, there is typically no distinction between rimmed and unrimmed cartridges, unless one is referring to a rimmed version of a cartridge which is typically rimless, such as the .45 Auto Rim, a special rimmed version of the .45 ACP ("Automatic Colt Pistol" aka ".45 Auto"), intended for use in M1917 service revolvers.
