Spec Ops: The Line

Though this is simple to gain through natural play, blind firing isn't an often occurrence and some may miss this. If you did, load up Chapter 6: The Pit (chapter select lets you have 4 separate saves, so you don't have to worry about losing your current progress).

Once the cutscene is finished, run to the right where you will find a shotgun leaning against the wall of an enclosure. With a dozen plus enemies dropping into close quarters with you it is very easy to blind fire them with just one shot.

This isn't particularly hard and I'm sure you will get it without even trying. Essentially it's just killing 5 enemies cumulatively across the game with blind fire.

I've made a video of when I got the achievement so I hope this helps.