Does anyone have any tips for learning how to get headshots better? I got hung up on one of the Undead Nightmare challenges with getting (if I remember correctly) 5 headshots in 8 seconds with the sniper rifle and without using deadeye. The reticule is so small and the zombies seem to move right as I pull the trigger. I don't have problems with headshots in FPS (and usually prefer sniper rifles)...but in RDR it's miserable to me. Does anyone have any advice?