Got this with the help of iTz Canada Ehh's guide on TrueAchievements.com. The trick to me was using explosive arrows and having my bow equipped with the Marksman sight. I made 10 of them, located a high spot above an outpost and used my camera to mark the targets. Save your game and start firing those explosive arrows. It took some trial and error (I ended up using the 80m marking as the 100m marking made my overshoot my targets every time. Hope this helps someone and here's a link to where I got my info:
https://www.trueachievements.com/a253131/toxophilite-achieve...