Welcome to the Forum. Based on the serial number, the gun is a .32 hand Ejector. 3rd model, as said by P&R Fan above. Close serial numbers were shipped in 1920. Actually the gun is a "5 screw" model to collector. as the 5th screw is the one in the front of the frame below the barrel. The 43598 number is the work/assembly number used to keep parts together during manufacturing and has no relation to the serial number. You say you had to remove the grips to see the serial number, so you must have the target style grips that cover the butt of the frame. They would be an additional accessory and may, or may not, have been on the gun when it was shipped from S&W. Your gun has the heat treated cylinder and would be safe to shoot with smokeless ammunition, if it's in good mechanical condition. Congrats on your first S&W - now you will soon become addicted! Ed.