Reflex training. Back to a target. On "Go" spin to face your target, aim, fire. What sucks is that the target will most likely be static. In paintball I used a rocker trigger sometimes which is good for rate of fire, but not necessarily for finding the target and the initial shot. If you have a semi auto gun and no rocker trigger, use a real loose grip and use your middle finger to rapidly 'tap' the trigger. Again, rate of fire thing. Not quite for developing better reaction time.