How do you attach a sprinkler valve to pvc as they are usually metal aren't they?

Sorry for all the questions but this is my first pneumatic spud gun.

Do you guys see anything wrong with me using pressure rated PVC-U for it?

Is there any way of using abs and pvc in one cannon as I have heard that ABS does not shatter if the chamber ruptures?

I am considering making a pneumatic potato cannon. It would be made completely of PVC-U. The air chamber (if thats the right name to call it) would be 4" and the barrel 2". Is it safe to use a 2" Ball Valve instead of a modified sprinkler valve. Also the PVC is pressure rated to 130psi does this mea...

I live in the UK and I really need help finding a 4" cleanout adapter and plug. I know you can buy them in the US but the shipping is about $90. If you know of any websites where I can get them without the huge shipping cost please let me know.