Garrett, the serial number on your uncle's Browning Auto-5 indicates two things. First, it was made in 1954 and second it would be considered a Standardweight version. This shotgun would have actually been made by Fabrique Nationale (FN) in Herstal, Belgium. The barrels should show a "St. Louis, Missouri" address to be correct for the year of production. In excellent condition the shotgun with a plain barrel could be worth about $400-$470 with premiuns added for those with either matted rib or ventilated rib barrels. The extra barrel could add about another $100-$125 to the overall value with the 'correct' address. Hope this helps!
Steve Mace
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After today, its all historical