I finally got this project off the ground. It took me forever to find stuff at the hardware stores that were proportioned correctly. The barrels and outer ring are slightly larger relative to the stock than the concept drawings suggest, but not by much. I had to find a happy medium on the over all size. However, ive stayed closely to what the drawings and sideshow have done. The outer barrels are 2.5" pvc. The inner barrels will be 1.75". This conviently is also the diameter of firework motar launching tubes.
The bottle in the last picture is for size reference. The side show replica weighs in at 42lbs. This one will round out about 15 lbs. It still has a ton of work to be done. I started to shape the stock out, but got sidetracked and put it together for giggles.