The 40914 is the work/assembly number,not the serial number. It was used to keep parts together during manufacture and has no bearing on the gun's identification. The serial number is on the grip butt, on the back of the cylinder and on the barrel. The letter "C" on the butt and is part of the serial number. If the gun is an original US Airforce M-13, it will say " Revolver Lightweight M 13" on the top strap and "Property of US Air Force" on the back strap. S&W logo on the side plate. "P' stamp on the left side of the frame above the front of the trigger guard. Can you post some pictures? Ed