The answer that I will supply you with,will be based on your shotgun having between 60%-90% of its original finish remaining,and a good bore.If your shotgun has a standard barrel then it is valued at between 340-450 dollars.If your shotgun has a vent rib barrel,then the value will be between 415-630 dollars.
1943 browning light 12 belguim made $5K
What is the value of a 12 gauge Browning shotgun serial J68824?
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If you mean a Browning B-2000 12 gauge shotgun then the value would be 495 dollars for a shotgun in the condition you describe.
http://www.browning.com/products
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Browning never made a Model 51 shotgun.
100-1000 USD
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100-2000 usd
0-400 usd
50-700 usd