It is made with;
1 2 inch barrel
1 4 inch chamber
2 4 inch couplers
2 4 to 2 inch reducers
1 2 inch female threaded adaptor
1 2 inch threaded plug
2 1 inch PVC slip on pipe caps
1-1/2 inch PVC pipe
2 o rings
1 fill valve
1 lawnmower starter cord
1 screw eye bolt
1 golf ball
1 Poof foam Football
In assembly, the barrel had rectangular ports cut into the side next to where the rear reducer is located. and then assembled into the chamber barrel assembly with a fill valve stuck in the side to create a weak point of failure. In assembling the barrel end, the end became stuck and I didn't get it pushed all the way together. Now I have two possible points of failure to watch. It is now more dangerous than I originally planned.
As always, it is not a good idea to use non pressure rated pipe for air cannons. Test your materials safely. To seal the barrel a valve core was needed. Having worked with PVC before I made it from PVC. The core is easier to make than it looks. It is made from 1-1/2 inch PVC pipe, 2 1 inch PVC slip on pipe caps, and 2 O rings.
To make this core, the PVC pipe was heated and shoved onto a pipe cap. The cap was removed and a 1/4 inch was cut off the end. The ring was glued on the pipe cap, followed by an o ring and the pipe again. Making the o ring groove was that easy. The process was repeated for the other end of the piston. A hole was drilled for the rope. Added a couple flattened pieces of PVC for washers and the foam core from a foam football was used for a bumper. To finish the end cap was drilled for the trigger lanyard and the golf ball added to finish it off.
On the steel upgrade in the back, I stuck to a golf ball trigger.
Knowing ABS tends to split out the side when it fails, I stood behind it and filled it to 85 PSI. It held. After several fantastic shots I took it with me to a church camp where they have apple trees. Using fallen apples it is used every year at up to 65 PSI after the annual 85-90 PSI test. This is my oldest functional air cannon that has outlived several PVC cannons that cracked, developed leaky joints, or plain failed.
This cannon has a typical range of 525 feet with fallen apples and has split a 2X6 8 feet long.
Due to the bulk of the chamber, this cannon is a very poor single person hand held, but it makes great mortar shots. Load it, stand it on end, step on the rope between the cannon and golf ball, grab the blue trim and lift.
Never ever load one of these while under pressure. Loading does the same thing to the core that pulling the rope does. 
It has taken abuse that kills my PVC cannons.
