You Are The Weapon Achievement in Halo: The Master Chief Collection

Though this achievement can be completed on any mission that houses a duo of Hunters, The Silent Cartographer is probably the best mission to attempt this achievement. On this mission, once you are required to head on over to the security control room, you will fight a decent amount of Covenant troops while ascending a grassy hill. After this firefight, you’ll find yourself in an open valley where this mission’s terminal is located. Here, you’ll also find a nasty pair of Hunters ready to attack.

Since you begin this mission with a Magnum by default, it is important that you kept it up to this point. When facing off against the Hunters, you’ll need to position yourself a few feet directly ahead of the creature. At this point, the Hunter will lunge forward and charge at you. When they do this, you’ll need to sidestep to the left or right in order to dodge the assault. Quickly turn around and aim your Magnum at the patch of exposed, orange flesh on the Hunter’s back. With a single Magnum shot at this weak spot, the Hunter will immediately topple of to his death, thus unlocking the achievement.