and the fullsize image
http://www.laredoperformance.com/cannon1.jpg
Obligatory gf with cannon shot:

For the spacer between the chamber and barrel I used a 2" peice of pvc cut down the middle, flipped back to back, then 2 4mm socket head cap screws + washers + nylocks in them. I think I'm going to end up slotting each one, so I can use 2 hoseclamps instead of one giant one. Which would make some sense, considering the barrel is removable. Let me know what you guys think.
*Edit*
Forgot to add some specs, silly me.
24" 4" sch40 pipe for the combustion chamber. With all the fittings, it works out to just shy of 5,500mL. The barrel is 57" of 2" sch40, measuring from the end of the male fitting, to the bottom of the first muzzle break hole. It's actually 6" longer counting the muzzle brake and the knife-edge. Holes are 3/8" diameter, 5 rows tall, 8 wide... should sound funky. Most muzzle brakes I've seen don't use that many holes. Sorry, went off on a tangent...
C/B ratio with that barrel is about 1.8. I think that might be a bit on the EXTREMELY LOUD side, however, I'll be able to change them out pretty quickly. Let me know what you guys think so far.