After a cutscene around the middle of Mission 2: The Battle Of Endor (after completing the main objectives in the starting are), you will see some enemies in front of a bunker. Inside the bunker is the "Barrage" in a weapon box. It looks like a grenade launcher. Grab it and press D-pad Left to equip it. Then, proceed to the next main objective (kill a bunch of enemies in the woods). There will be a lot of enemies spawning close together. It is easy to kill five of them with one hit. However, you only need to kill five enemies with three shots to get the "Balance Point" achievement. The Barrage has three shots. Restart the checkpoint to try again if it fails.