This achievement will probably come with natural progression if you use the rogue stance a lot. If you want to knock this out early, you can get all 200 during the training. Simply walk up to the soldier to the left of the door on the right to begin rogue training. When you begin, simply press RT to shoot at the soldier. Repeat this 199 more times for the achievement. Your pistol overheats after a few shots. Also, pressing RS to lock on to the soldier will make this a lot easier. You can't die, so don't worry about missing shots or getting hit.