Whilst fighting Reed he does not recover whislt on the grass, mount a horse as this helps to protect you and slowly walk up the ramp once Reeds head is just in view shoot him with the snipe rifle and quickly run back and hide by the wall jump off the horse and run after Reed shooting hime with the normal rifle in the head if possible make sure reed dosnt stop for too long if at all on the sand as he will recover repeat this and you will soon been rid of him.