Peekaboo...I Shot You! Achievement
Peekaboo...I Shot You!10
Kill 50 enemies with the sniper rifle.
Most of these achievements will most likely come with natural progression through the game. You will be changing weapons on a regular basis through the game so these may be difficult to keep track of. If you want to earn a fair amount of kills with each gun always kill an enemy with a headshot. Most enemies will take a single shot to head so you can conserve your ammunition.