I checked the 27th edition Blue Book and it stated that the FWS prefix was for production from 1946 to 1950 and Marlin production from 1968-73 had a FWM prefix and the serial number 25xxx fits into the 1946-47 timeframe. I still am curious about the patina on the barrels. I also checked the values for the field grade guns and I guess that my $175 was well spent.