I dont have any photos... so a MS paint drawing will have to suffice.

This setup is not to scale.
I used 1'' x 1' galvanized pipe for the chamber, a 3/4'' brass ball valve for the firing valve, and a copper AA battery barrel of about 2.5' in length.
the gun was pressurized to 550 psi with my fridge compressor....
ball valve held shut with a block of wood that pivots, and acts as a stop direct-ally on the ball valve handle.... press the block like a trigger... and the spring opens the valve.
Now, seeing as this is my first ball valve cannon... i had no idea what to expect... certainly not the loud crack, and massive amount of recoil that i ended up with.
After bouncing off of a plate of 1'' thick steel, the AA battery proceeded to break a 2'' diameter (best guess) limb from the top of a tree across the field. (about 100 feet from me.)
This gun actually scared me... and i almost dropped it.
Has anyone with a spring powered ball valve taken one up to 550 psi??
This is by far, my most powerful cannon yet. and the loudest.
Seeing as my stash of dead AAs is growing... what do you propose i shoot next???