SpudFiles

This is the potato cannon I made:
4"x18" chamber
4" Cap
4"x2" reducer with 2"x1.5" bushing
1.5" ball valve
1.5" Barrel
Screw in schrader valve

Only suggestion I have is to lengthen the barrel because you are using a BV. That giant BV must be a pain to open so I would stick like a 5 ft barrel on and you will get WAY better performance. Also, that reducer isn't rated for pressure, so stay around 70 psi max. Oh and also you should have screwed the schrader in where there is two layers, so be careful.

Defiantly lengthen the barrel, also you left you the extra pipe so just cut off the DWV reducer, and you taped the schrader into a single layer of pipe. Other than that its a decent first attempt

Ya the barrel should be longer, do you think that I would get a lot more range out of a longer barrel? And as for the valve the threads weren't long enough to go through the cap and pvc. I think it should be ok because it has a shoulder on the inside.

You will get a giant power increase, I would at least double the barrel length

The reason the ball valve and a short barrel is a bad combination is the time required to open a ball valve by hand is too long. By the time the valve is partially open, the initial flow will eject the projectile out the short barrel before you get any real force on it, resulting in low power shots.

A faster valve ( some here use springs with good results ) or a longer barrel makes a big improvement. Having the projectile still in the barrel when the valve is fully open helps a lot. A longer barrel makes it possible.