Very decent and detailed info Legolas but.......
He's using the Baldurlash grandmaster patch which gives +5 damage when grandmastery with a particular weapon.
The latest BG2/ToB patch actually reduces the damage from a composite long bow to +1
Total damage should therefore be:
1D6 arrow
1 Composite long bow
3 archer kit
5 grandmastery
=max 15 damage [img]smile.gif[/img]