My knowledge of crossbow feats is poor at best. What's giving you the 2.5*Dex Mod at level 6?
Crossbow Sniper gives half dex to damage with crossbows in addition to raising sneak attack range to 60'. Vital Aim just gives dex to damage with ranged weapons. Deadeye Shot gives Dex to damage within 30' if the enemy isn't immune to sneak attacks. The sum total is 2.5*Dex to damage within 30', 1.5*Dex outside that range (or against sneak attack immunes).
JaronK
Is it the Deadeye Shot from PHII? Because that one just says that the target loses their dex bonus against my attack.
That's what I thought as well. But I did some digging and there's a feat just called Dead Eye in Dragon Compendium I (originally dragon #304).
[spoiler]Your precision with ranged weapons translates into
more telling strikes than you could normally make.
Prerequisites: Dex 17, Point Blank Shot, Weapon
Focus (any ranged weapon), base attack bonus +14.
Benefit: You may add your Dexterity bonus on
damage rolls made with ranged weapons for which
you have the Weapon Focus feat, so long as the target
is within 30 feet.
Special: Dead Eye does not increase the damage dealt
to creatures immune to critical hits.
A fighter may select Dead Eye as one of his fighter
bonus feats.[/spoiler]
edit: Which unless I'm missing something means it can't be taken at that level as it has BAB +14 as a requirement.
edit2: The one in dragon 304 has bab+1 as a requirement.