Maybe if the flap in the cardboard were cut so that the "hinged" side was on bottom, it would work better. You could attach the pin as well as a lead weight to the flap and let gravity help you pop the balloon. As long as the cardboard is a snug fit against the moving part it will stay up, but when the projectile hits it there should be enough energy transfer to put the flap in motion.

I'm glad the flour thing worked out..........it would be interesting to see. [sm=thumbup.gif] Maybe when you get it all perfected, you can make a short video clip.

Jason