Quantum Theory

To unlock this achievement, you must perform 200 headshots. I suggest picking up the Plasma Lancer whenever possible, this and the Revenant are the easiest weapons to get headshots with. Most of the time when a headshot is performed correctly, the camera will zoom in and you will see, in slow motion, the enemies head exploding. But regardless, when an enemies head explodes, that is when you know you have performed a headshot correctly.

I hope this solution helped! Leave a comment letting me know if there is any room for improvement! Thanks.