I do not want to restrict any creative juices and understand that this was not the original idea, but wouldn't putting any type of projectile firing mechanism that fires past 100fps on a moving plane rather dangerous (No reason why I picked 100fps, could be higher or lower). From what I learned from previous sites was that airsoft guns fire projectiles around 300fps. Although I know that as airsoft pellet does not have much mass, it still has the potential of being rather dangerous without very careful behavior. Just in case someone actually might want to go outside and try this, although there are videos already on youtube of people doing this stuff.
of course there is the possibility that I am wrong, but I think it is better to be safe.