How I did The Sharpshooter 9 Challenge
1.Find a Lemoyne gang camp
2.Steal one of the horsie. Make sure they sees and take shots at you.
3.Speed ride the horse away from the camp until the Lemoyne camp..."Reset".
4.Ride back to the camp and the Lemoyne Raiders will not be hostile (bug).
5.Take all time in the world to complete the challenge.
Other challenges that should work using this technique...
Weapons Expert...
1.Kill 3 enemies with a knife.
2.Kill 3 enemies in 10 seconds using only throwing knives.
3.Kill 4 enemies at the same time with a single stick of dynamite.
4.Kill 4 consecutive enemies by throwing and retrieving the same tomahawk.
Sharpshooter
1.Kill an enemy at least 80 feet away with a thrown tomahawk.
Bandit
1.Hogtie someone and leave them on the railroad 3 times
2.Steal 5 horses and sell them to the Horse Fence at Clemens Cove.
...
https://www.youtube.com/watch?v=Hd_XmN9O5p0