Beginning in 1868, thousands of black powder Colt revolvers and Remington percussion revolvers were converted to cartridge revolvers. Among them: the 1851 Navy, 1858 New Army, and 1860 Army. Remington was the first to introduce single action cartridge conversion revolvers in 1868. The original cap-and-ball cylinder of the 1858 New Army cartridge revolver was replaced by a cartridge cylinder with a loading gate and a new breech face. The frame was dovetailed to accept an ejector assembly. The Remington conversion chambered five, .46-caliber rimfire cartridges. In 1871, Colt received an Army contract to convert one thousand Model 1860 Army percussion revolvers to use the .44-caliber centerfire cartridge being manufactured at the Frankford Arsenal. In 1872, Colt began filling civilian orders for thier metallic cartridge revolvers. These were an open-top conversion of the 1851 Navy. The next design was introduced in 1873, when Colt produced the Richards-Mason conversion of the 1860 Army. Using a system patented by Colt employees Charles Richards and William Mason, the old cap and ball cylinders were cut down at the back to permit the installation of a conversion ring to accept metallic cartridges.