Deathbringer is a Gun Perk in Call of Duty: Infinite Warfare. When a double kill is scored with a weapon that has this perk, its magazine is instantly refilled. This does not deplete your stored ammo. Note that the weapon does not necessarily need to provide both kills for Deathbringer to activate; as long as it is equipped for the second kill, the magazine will be refilled.
In Zombies, Deathbringer activates after a quadruple kill instead of a double kill.