The projectiles on the far left are actually shot out of the cannons 1.5″ barrel, except for the end cap which is screwed onto the end of the barrel, after the barrel has been filled with water, to make the cannon a giant water gun.
The tube in the middle does not get shot out of the barrel. After experimenting I made a very tight fit with the tube in the barrel of the air cannon. This allows me to exeed the volume of air ratio so I can shoot Nerf darts and wooden dowel rods across my 4 acre yard.
The tube on the far right uses the same principle of the previous tube but is bigger and longer. This means I can launch more specialized rounds farther down range. The pictures of the finished projectiles are farther down.
Hopefully, in the future I will build a universal receiving platform so I can continue researching in a more professional way.