Killed two enemies with one bullet in the Changing Tides mission

This achievement is pretty much scripted. During Mission 5: Changing Tides, you come to a part where your teammate asks you to take out both enemies using 1 bullet. Just wait for the shot to line up and take them out. If you fail, feel free to restart the checkpoint. NOTE: There are multiple ways to get this achievement, but this is the best way, especially if you are playing on hard.