Long time ago on PaintballMontreal, someone just showed us how to build-up piece by piece a rocket launcher for NERF if I'm right. It was an invention from the guy and it was doing great. Some other people did it so it wasn't a piece of crap.
Only hicky thing.. 1 load of a .12g of CO2 per shot.. So in a tank.. you must have a gooood number of them.. =P