ha ha we did the same thing except we used a big ass coffee can and a long cardbord tube, about the same amount of duct tape, we used oxy acetline as our fuel and used balls made from used paper and masking tape for our projectiles ours shot about 200yards and lifted the little fella that was holding it off the ground, were lucky he didn't get blowed up...
what is the horn blowing right before you ignite it or is that the ignition before the blast,
We launched a 2 liter of soda today. The first attempt almost blew my hand off. So one 3/8" piece of flat steel welded as a back plate later we can get >1000' with ease, but it takes 3 people to hold it.
The lack of tape allowed us to move to acytelene and oxogen......HOLY SHIT is all I have to say. It may have cracked teh windsheild of the truck parked next to the explosion (we are unsure if it was an existing crack).