Oh wise bow hunters, what mythic skill you have attained to! I would bow if I hadn't lost both of my knees to your most accurate shots. Alas, since your most skillful rendering of myself a cripple, I can no longer partake in adventures with all of you.
I did it by doing one of those wanted dead missions so that it would show the range to the objective. I stayed 95m away from the leader and went for one of the charger guys nearby. I had to aim like 3 inches above the dude's head to get that achievement. --- GT: Obstreperosity "Zur-En-Arrh"
When you first see Hoyt and he drives the three guys into the minefield, two guys are standing over the range needed to get the achievement. Two guys standing next to each other, I got it by accident trying to hit them with an explosive arrow that turned out to be a normal arrow and I just wasn't paying attention.
If you miss just keep restarting from checkpoint and taking another shot. --- People who want another SW Battlefront: 216 "Gnarly, you are clearly more educated than me" - OblivionScamp. GT: Charlievil
I got mine on a shore before you enter a certain story-related cave, and was aiming for a specific guy. I was also, apparently, aiming slightly too high as the arrows go straighter than I thought, and I end up nailing the guy about another 10 yards behind him when the achievement popped. --- XBL GT: Gigantopithecus
They need one for over 100m. I do those all the time.
EDIT: Before people think I'm bragging I've only done about 3 outposts so there are a ton of people roaming the roads. Just line one up and you should be able to take out the other two after the first one drops.