When I first started making spud guns, I made the simple combustion one with the bbq igniter. I was so excited to see the little blue spark down the barrel from the bbq igniter, and assumed it was okay to look at since the cannon had never even seen any fuel. But, I had just finished making the thing and apparently the fumes from the glue built up in the chamber and shot a fireball straight at my eye. Good thing back then I wore glasses and all I got was a little burn ring where my glasses were, and lost an eyebrow. Moral of the story: Do not EVER look into the end of the barrel, and when you are done making the thing, set it aside for 24 hours. I don't care how excited you are to see it fire!