Colt tasked its superintendent of engineering, Charles Richards, to come up with a solution. The Richards conversion was performed on the Colt 1860 Army revolver. The caliber was .44 Colt and the loading lever was replaced by an ejector rod. This conversion added a breechplate with a firing pin and a rear sight mounted on the breechplate. Cartridges were loaded into the cylinder one at a time via a loading gate. Colt manufactured 9000 of these revolvers between 1873 and 1878. In 1873, Colt performed the same conversion on the M1851 and M1861 revolvers for the US Navy in .38 rimfire. Another of Colt's engineers, William Mason, improved this conversion by placing the rear sight on the hammer and, along with Richards, he was granted patents in 1871 to convert percussion revolvers into rear-loading metallic-cartridge revolvers. Those converted revolvers are identified as the "Richards-Mason conversion". There were approximately 2100 Richards-Mason M1860 Army conversions made from 1877 to 1878 in a serial-number range 5800 to 7900.