Highly recommend you leave this to someone who has had training by Browning. If you attempt to do this without the right tools and knowledge, you run the risk of causing damage. You might only mess up the appearance, but, you might compromise the safety of the weapon.
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.