Here in france we haven't sch40 pvc and i didn't want to spend extra money buying it from another country.
The air tank is a 20" x 1.5" copper pipe, which is stopped by a 1.5" elbow and an brass endcap. all the pieces are superglued, as superglue can handle much more than any of my spudguns would ever take. I usually pump it to 5bars (80psi) and it shoot pretty well, with some noise.

My barrels are a 1/2"(1m) , a .40 cal which is small (30cm) and a potato cannon, 1.5".


Here is the adaptor i made for the .40cal, it's made from electrical conduit pvc .the ring is for the adaptor of the sprinkler valve.


And this is what it looks like when aiming.
This canon is great for it's small size. it's powerful and can reach up to 700 fps with marbles (3 grams , 16mm).
I am currently thinking of adding a blow gun for trigger-style actuation, unfortunatly my last blowgun had a too small flow and didn't open the valve quick enough. For the moment, i am using a ball valve actuation for the sprinklr valve.
I will soon get a 3/4" barrel for paintballs!
You will excuse me for my poor english, i'm trying to do my best (i'm 17 yrs old french guy!!)