You get this in the "Questions and Bullets" chapter (~chapter 15). After initiating a conversation with the man in the shooting range, you'll have two opportunities to take target practice.
The exact win conditions for this achievement are not as clear as some of the others, but basically you just need to shoot well, avoiding civilians and not making too many misses. It's fairly easy to begin with but gets faster and faster until its nearly impossible to hit a target.
The achievement doesn't unlock until after the second round of shooting (there's a conversation in between).