Prerequisites
Dexterity 13.
Benefit
Once per round, you may make one additional attack with a ranged weapon with any standard action attack or full attack, but not when using a special attack or maneuver (such as the Manyshot feat). The extra attack is made at your highest base attack bonus, but all attacks you make in that round (the extra one and the normal ones) take a -2 penalty.
Special
If using a repeating crossbow, you may make one additional attack when making a full attack, giving you a total of two extra attacks; however, this second extra attack suffers an additional -5 penalty to the attack roll.