From publisher blurb:
Master at Arms kicks off with the arbalestier, a master of the heavy crossbow, and a true "one shot, one kill" specialist. No longer does the heavy crossbow need to be the poor cousin to the longbow, relegated to a backup weapon for sorcerers and wizards when they run out of spells. The arbalestier combines increased damage, armor piercing capability, and other innovative abilities to make the heavy crossbow a viable choice for ranged enthusiasts. So look at a long-ignored weapon in a new light with Blackdirge Publishing and Master at Arms: Arbalestier.
Master at Arms - Arbalestier includes 6 pages of new d20 material, which includes the following:
A historical look at the heavy crossbow
Author's design notes
The arbalestier prestige class
Bregek Ironprod, a sharp-shooting duergar arbalestier