My latest cannon has a combustion chamber. I use 4 inch pipe about a foot long. An adapter down to 1 1/2 inch. A threaded end piece with a threaded cap holds the ignitor. I load from the muzzle, spray in the chamber, slap the threaded cap on, aim, spark...Click!...Fizz...Ka-whomp!!!!
No joy!
No spark from the igniter I'm using, but boy did I get a spark from my better half when she got to wondering what I was up to in the garage!
I'll have to put this project on hold until she visits her mother next month.
heh-heh-heh