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.
1971
If you go to browning,s home page there is a way to age your shotgun there.
BT99
Browning doesnt show the BT99 as a 299 model code. They list the BT99 as a model 149. Below is the link to the Browning codes.
There should be more numbers and or letters in the sn. If not, call Browning.
100-1000 USD depending on condtion and EXACT configuration, papers, box, accessories.
Japan
Please add the serial, but it is likely a single barrel trap gun such as the BT99
A shotgun designed to shoo trap with.
100-1000 usd
1988
2003