You'll need to purchase and equip the Recurve Bow (K 60,000
) and Marksman Sight (K 32,000
) in order to make this achievement a lot easier.
Now you can use the map to fast travel to any previously liberated towers or outposts, and then you'll want to choose any outpost. Go to that outpost, and approach it. Use your binoculars to mark some enemies, and use the distance to the outpost as a reference for your distance.
You'll want to line up your arrow and use the markers in the scope to compensate for arrow drop. Just line up your shoot, and kill the enemy from 60m or more to unlock the achievement. If you miss or are spotted, you can die and respawn at a checkpoint to try again.