This particular one was done for a fee and is now on permanent display in a middle school. The guy makes his living as a professional musicial, apparently of some renown. There's other stuff of his on youtube, including his quadrapult (four shooter), and what I consider much harder to construct, his rotapult (one shooter). Look on youtube.
Personally after looking at this a few times, and looking close, it shouldn't be near as complicated to duplicate as it looks. The really hard part was thinking it up and making the first one, but even then I think the rotapult was harder. I've got it pretty well figured out but one or three pieces, once I get them figured out I think I'll try one, or at least try to start on one.
:rotflm: