when fighting reed he dosnt regain health whilst on the grass so you need to bare that in mind !!! so you need to mount a horse and slowly walk up the ramp toward the grass select ur snipe rifle aim it at reeds head shoot him and quickly run away and hide down by the wall, jump off the horse and chase reed shooting him in the head with your normal rifle as long as you dont let reed get out of your sight and stop for to long on the sand he wont regain much, if any life at all, repeat this and soon he will die ! good luck mate !!!