Value is too difficult to be accurate without seeing the gun. Condition which includes the amount of original finish and original configuration will determine value. Recommend taking it to a gun shop for appraisal.
BT99
Japan
100-1000 usd
2003
1971
1988
You must call Browning as the sn you gave does not follow normal convention.
100-1000 USD
If you go to browning,s home page there is a way to age your shotgun there.
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.
50-650 usd
Incomplete serial number. Get the complete number, go to Browning's site, Support, Date Your Firearm. They have a complete listing.