High Quality Content by WIKIPEDIA articles! The .45 Colt cartridge is a handgun cartridge dating to 1872. It began as a black powder revolver round developed for the Colt Single Action Army revolver, but is offered as a magnum level handgun hunting round in modern usage. This cartridge was adopted by the U.S. Army in 1873 and served as the official US military handgun cartridge for 19 years. This cartridge is often referred to as the ".45 Long Colt", though this is just a colloquialism.