Build a gun that uses gas expansion ignition from alcohol for propelling projectiles such as BBs.
This project gives you a glimpse of how old muskets work. Since gun powder is too dangerous, we'll work with handwash alcohol.
How to use it:
First, open the barrel. Spray your fuel in the combustion chamber. You are free to experiment with different combustible liquids but "Denatured Alcohol" works best for me. Next, chamber in your projectile in the barrel. You can use all sorts of projectiles but due to safety reasons, better stick to paper, seeds and BBs. You can use some cotton to hold your projectile in place and having a better seal with the barrel.