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1971
BT99
Please add the serial, but it is likely a single barrel trap gun such as the BT99
Japan
A shotgun designed to shoo trap with.
1972
Believe that your serial number is incorrect. There are no BT99 serial numbers that start with 47. There are however serial numbers that begin with 74 which is the year (1974)that they were made.
100-1000 usd
2003
1988
100-1000 USD or more depending on specifics