Aerosol

Aerosol propellants come in cans, you can buy them at any grocery or department store, and they do not need any auxillary hardware (like a fuel meter) to use. As such, they are quite popular.

It is recommended that you avoid using hairspray, as it will gum up your chamber. Deoderant is much better - "Right Guard" in the brown can was the generaly recommended one until recently, when the formula was changed to use a non-combustible propellant. Any spray with flammable propellants will work, look for things like propane, butane, isobutane and/or ether).

Because the amount of fuel cannot be measured accurately (the usual procedure is timing the spray duration by feel), it does not yield the performance that metered propane does - the pressure generated during a closed chamber firing is estimated to about 30-40 psi, as compared to 40-50. If your cannon is not firing, or is firing weakly and you have a flammable fuel (verified by spraying over a flame): check the ignition source. If you are getting a spark, you are most likely spraying too much fuel in; play around with how much you spray in until you get a good bang. And always remember to vent your chamber between shots.