From Destinypedia, the Destiny wiki
The Bolt-Caster's special attack is Sword of Thunder, which fires a large lightning bolt forward. Bolt-Caster is the only sword with a ranged attack. This consumes five ammo to cast. It also comes equipped with an Arc guard for protection against Solar and Void attacks, and increased armor. Even so, the Bolt-Caster is widely considered the least effective of the three exotic swords for PvE, but is actually the best sword available for PvP.