I would think old tubes might work for that device- and I would recommend acorns or rocks as the projectile. Tough to shoot while riding though. Maybe it could be mounted on the bars so it could be launched with one hand?
No, you can shoot them while riding. Just aim for the right side of the acorn so it shoots out as you go over it. It works pretty well to hit cars to your left. An acorn has just the right size and slipperiness to squirt out.
(This is why I’ll be missing the oak trees on Forbes between Braddock and Beechwood this fall.)
The section of trail right next to the Casino rock/gravel parking lot is awesome for sending rocks sideways into the cars (that are responsible for kicking the rocks onto the trail in the first place) I’ve hit one car already, but that was completely by accident.