Heavy Fire: Shattered Spear

I got this while going for the 5 head shots in a row. Given the amount of enemies in this game and the required 2 play through minimum, you should get this without even really going for it (unless you just spray bullets everywhere). You should be aiming high when coming out of cover.

I have found that the game can have difficulty registering a head shot from time to time so aim for the crown of the head just to avoid it being a "neck shot" (for lack of a better term)