So, this German man named Joerg Sprave has a channel on YouTube (also a website: http://www.slingshotchannel.com/ ) where he makes weapons/toys that are legal in Germany which has restrictive weapons laws because he uses designs which under law define them as toys. In keeping with the slingshot idea, he tends to use rubber to power his creations, but also uses compressed air a fair amount. He has done some really interesting challenges and creations, and on top of that, he has a remarkably likable personality. I'd recommend his channel: https://www.youtube.com/user/JoergSprave