I ran across these and thought they were pretty cool. Must have taken some good craftsmanship to make them. I've always wanted to make a miniature cannon when I get the time/money/equipment...
http://www.darkroastedblend.com/2008/04/miniature-spy-guns-part-2.html
http://www.darkroastedblend.com/2008/04/miniature-spy-guns-part-2.html