Ahh, but Soda, it ain't being advertised as a training gun, but rather an less than lethal weapon. In that case I would rather have a 200 round hopper than a 15 shot mag. Even if the hopper sat on top of the gun and was therefore "untacti-cool".
I've seen George's paintball gun design. It is better than this thing.
Plus if you are going to make it so that your gun only fires strange rounds and hold 15 shots, why not make it .80, .90, or .120 caliber? Since you are depending on the ball to deliver a payload, why not send an enormous payload?