Since the video I just put up (see the post below) has already vanished, courtesy of the BBC, here’s another one. This is what happens when mischievous boys have too much time on their hands . . . and access to a hardware store.
Looks like fun!
I'm thinking it needs improving. Make the magazine vertical, with a spring-loaded flapper to stop the balls from entering the air chamber. That would make it gravity fed, instead of hand fed. Maybe a container at shoulder level with a flexible hose to the y-connector. Possibly 2" vacuum cleaner hose.
My dark side is thinking of hard-frozen ammo…. Ouch.