Looks dangerous. Probably is. I found this streetuse weapon on Matthias Wandel's website, where in addition to the air gun he documents his other benign and geeky pursuits, including what he calls his "insane contraptions." He writes:
Air guns are normally small air powered rifles that shoot relatively small projectiles, primarily used for target practice. Usually, they are pumped up with an internal cylinder, activated by hinging the barrel towards the stock. My home made air guns experiments however take their lineage more from potato gun technology than target practice rifles
The nice thing with an air gun like this of course is that it can be used to shoot all kinds of stuff. AA batteries, for example. Or Pens, or sticks of wood. Or filling the barrel with water. One Idea I got relatively late was to try to shoot the big chocolate covered peanut M&M's. They are about the shape and size of a marble, but not as heavy, and not as round. I wasn't expecting to put one through 1/2" plywood, but I figured with 1/4" plywood, I'd have a chance.
The Wasp sucking machine in action on my roof. This machine was the fulfillment of a childhood fantasy!