Never thought about using PVC tubing what size and schedule?
I made mine out Of Aluminium tubing and had a friend weld them up. Then I took the time to design a firing mechanism that would fire a shot. If I was going to do this again I'd just call Zinger winger and buy his firing mechanism. I tried model aircraft electronics with earlier wingers and different firing systems like having a weight slide down a rod then hit a trigger and fire a shot and the bird at same time but too unreliable.
Now I use Tri-tronics but have thought about changing to Dogtra just have to change a few things from solenoids to servo motors.
found they were costing me about $300 each to build, it's amazing how all the little parts can add up and trying to find good pulleys and then when trying to buy latex tubing only buying a 100 ft a time, all these suppliers want to sell 1000 ft minimum.
But in the end it is rewarding to know that you made them yourself.