Prof. Evil and I experimented the other day with making squibs (bullet hits in movies). We started with gunpowder (Bullseye to be specific) ignited with a model rocket engine starter.
This was 1.2gr of Bullseye taped down with packing tape.
Then we tried with a couple more grains...
Then we took a short piece of metal rod, drilled a hole in the end and added the gunpowder.
Then we tried 5 grains taped down with duct tape.
Then we made the hole in the metal pipe bigger.
Finally, PE dug the parachute-kicker charge out of the top of a model rocket engine.
We still have more experimenting to do. I think without the proper container for this, we won't be able to get enough pressure to make it pop as well as being able to control the direction.
Either that, or we go with compressed air, which seems to work really well and is much safer. No fun in that though! [:D]