The easiest way I found to gain this trophy was by equipping the Recurve Bow with the Marksman Sight attached that shows different distance markers. Fast travel to Rochan Brick Co. Shipping (left of Chal Jama Monastery) and start outpost master. Once started, you should see an enemy directly in front which is the required distance (use camera to mark if necessary). Kill him and the trophy will pop. Might take a few tries if your not familiar with the bows like I was.
Hope this helps.