I am often amazed at what someone can construct with just a little bit of know how. Adding a little Kung Fu to it all jazzed it up some.
Directions on how to build them are at this link but please note: I am supplying the link only as an educational point of interest (as educational reading material) and am not advocating or even suggesting that you try to build one of these yourself (as they are probably inherently very dangerous) and as the guy in the video says - this is not something for a novice to attempt. In other words - I strongly suggest not trying to build one or more of them and must say - don't try this at home kids or adults. By going to the linked site you assume all responsibility for your own handling and or use of the information on that web page, anything you do with it and for any result:
Heck, you might even call them fire-arms!
All the best,