The mechanism came from a discussion I had with someone at London 2600 around 2006. He did send me some lego-cad shots, but I don't know if they were his, taken from someone else, or if he eventually uploaded them. The instructions were later found here. But I don't know if that was him, or someone else.
I also presented (a new and modified build of) the gun at Bacon in 2012, as part of the LEGO Punk talk.
Marquis de Geek