All charged upG 25

To unlock this achievement you simply need to kill five enemy ground troops in a single shot using the Titan Arc Cannon weapon. Ground troops can be either Grunts or Specters, but the five need to be clustered fairly close to each other. Shooting one trooper is enough, as the shot will arc to the other nearby troops killing them all at the same time. You will also need to be Level 21 to unlocked the Arc Cannon weapon.