I am confused by a featherweight 12 gauge field grade gun that I have. The receiver has a serial number preceded by FW as expected. The barrels have the same matching serial number but lack the FW designation. Can anyone explain this to me? I have a different non matching set of 12 gauge featherweight barrels that are of almost identical dimensions to the barrels in question that were bought from a parts gun and the serial number on these barrels is designated as FW. Both barrelsare Armor Steel. I don’t ever recall seeing this on any other guns. Thanks for any explanations in advance.