I would like to start off saying that this is not much of instructable as it is a design page. The type of mechanism for reloading is difficult to find on the internet. I am sure that if I looked hard enough that I could find five similar designs I did not thus I digress. This compressed air cannon base is simplistic, with special attention payed to the reloading mechanism. The reloading mechanism is comprised of a somewhat removable 10 shot capacity revolving drum magazine. The design is slightly crude and simple though it works. If you look at it closely there is a lack of PVC primer stains this is because I chose not glue the PVC. Sounds dangerous at first thought. The cannon is in an unfinished state a it is still being modified to achieve better performance. So why hasn't it blown up in my hands? Because the pressure of the air is all being held back by brass valves and a solenoid. The PVC is only briefly being stressed at each shot 400+ shots later it hasn't blown up. The rotary drum magazine mates on each end of the gap forming a continuation of the barrel as well as loading a new ordinance. Range testing with modified darts and a paper sabot gave a consistence of 580-590 feet with the cannon at a 45 degree angle and charged to 150 psi. This design is very rudimentary and still being tested and modified. If you have questions or comments I will try respond to them in a timely manner (a few days).
Things I might change/add/modify in the future in a new design:
Glue with primer
Change the frame design
Automate the rotation of the magazine drum with a stepper motor or 360 modified servo and a rotation sensor
Using a QEV (Quick Exhaust Valve) to increase performance
Refilling the main tank with a paint ball tank and a regulator.
More consistent darts and ordinance
Making a better seal between the magazine and the barrel
Handicaps and other problems:
You only get about 2 powerful shots before the tank needs refilling
The magazine doesn't seal very well to the barrel
Manual rotation of the magazine