Al Stahler creates these fireball throwing devices. I guess you could call it a gun. He uses propane and MAP gas as ammo. There are no actual projectiles other than the ball of fire and the movement of air. It looks really cool though seeing the small ball of fire spiral around inside the clear tubing and then it expands inside the large chamber. Creating a small burst of fire and air to knock down some bottles.
Al runs a small traveling shooting gallery he calls Fireball Shooting Gallery which you can follow on Facebook.
For those interested in how this works or how it is made check out this video tutorial.