Personally, I use butane. It doesn't leave residue and Is easy to induce using an old blowtorch without an ignition flint. Just open up the valve for 15-20 seconds and seal the chamber. Add the projectile and pressurize the whole unit using a broomstick to push the projectile into the barrel and pressurize the chamber. Finally, aim and fire.* Note: Never use a propellant that leaves residue, so for the love of god, don't use hairspray .