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.
Between 300-425 dollars depending on condition.
What is the value of a 12 gauge Browning shotgun serial J68824?
1000 USD
$350
Basically impossible to value a weapon with just the gauge and sn.
You will have to call Browning with the serial number to find out.
Not a valid Browning serial number.
Browning never made a Model 51 shotgun.
http://www.browning.com/products
100-1000 usd
Use the link below
1943 browning light 12 belguim made $5K