I have always looked all over the internet for plans to build one of these... but I have never seen any. so I built one! a breech-loading one!!!!
here is a vid http://www.youtube.com/watch?v=nAaJHNbEaTM
and here is another one poor quality though... http://youtube.com/watch?v=25uKNLOsyAY
sorry you cannot see the bazooka in the video,it was the first test and i did not hold it so that it could blow my head off!!! lol (now I hold it)