Robert, When you are looking up a serial # to determine when your gun was made you do not need to insert R (regular frame) FW (feather weight Frame) to get the date of manufacture. RE = regular frame with auto ejectors. The S indicates that the gun was made after Marlin took over the Hunter Arms Co in 1945 and all guns made from 1945 to 1950 have an S prefix. If you are looking up a gun with the S prefix you must include it with the Serial #. I hope this helps