Introduction: How to Make and Use an Air Cannon and a Smoke Ring Launcher
It is a cheap lancher that is great fun and the best part is that there is no need to reload, it's semi-automatic, because your ammo is air!
The demo on somke rings is here http://www.youtube.com/watch?v=KadUPdNB74A:
You can, in theory, change the smoke ring shape to a different one by making the hole that shape, but only simple stuff like hearts or triangles.
Sorry about the sound, it was done on a camera. you may need to turn it to max and put in ear phones. And sorry I kept saying "onion rings" - I was hungry, I meant to say "smoke rings".