Around 2,100 of these Colt Model 1860 Richards-Mason conversions were manufactured circa 1877 and 1878 as cartridge revolvers using a mix of percussion revolver parts on hand and newly fabricated components. They are one of the scarcest Colt cartridge conversion revolver variations and were manufactured concurrently with the famous Colt Single Action Army. The revolver has the distinctive breech plate without a rear sight, a "6" marked loading gate with external spring and a hammer with the added centerfire firing pin and notch rear sight. The barrel lug is a smaller lug, much different in appearance to the standard Model 1860 Army lug, and the slot has been filled and an ejector rod and housing mounted to the right side of the barrel. The top of the barrel has the one-line Hartford address. The two-line 1871 and 1872 patent dates are on the left side of the frame, and "44 CAL" is on the left trigger guard shoulder. It is fitted with a smooth one-piece walnut grip.