Manufactured circa 1873. This early production revolver was manufactured by Colt using unfinished and/or unassembled parts. This early pattern revolver lacks the external loading gate spring and two-line Richard's patent dates on the frame which were features of later production Richards-Mason Model 1851 conversion revolvers. The barrel is a partially completed percussion barrel. The revolver has the modified percussion cylinder with Richards-Mason breech plate, loading gate with internal spring, modified hammer with rimfire firing pin, ejector assembly secured by a screw on the left side of the barrel lug and ejector rod head with concentric rings on the face. The left side of the frame has the early "COLT'S/PATENT" marking. "36 CAL" is stamped on the left side of the trigger guard. The cylinder has the standard Colt Navy naval battle scene and "COLTS PATENT No." The top barrel flat has "-ADDRESS COL. SAML. COLT NEW-YORK U.S. AMERICA-." The inside of the loading gate is stamped with the assembly number "1317". The barrel lug, frame, trigger guard, back strap and cylinder are stamped with the serial number "597". The revolver is accompanied by a detailed description by previous owner John H. Thillmann. The description concludes: "This exceptional finished gun is in my opinion one of the top two Colt Model 1851 Navy conversions in condition". This revolver is illustrated on page 224 of "A STUDY OF COLT CONVERSION REVOLVERS" by Bruce McDowell.