I made my brother this gun so he could spud with me, and I was board. It is simple with a 80cm x 2.2cm chamber, and a 70cm x 1.5cm barrel. This is quite powerful for a ball valve gun as the ball valve, having been used on my QEV gun, has been used alot and is quick to open. I had all the parts already and only had to solder 2 joints and compress 5, as the chamber is my old barrel so it already had and olive on, so it took about 30mins to make. The wooden support is held with contact adheasive.
I personally would be comfortable with taking this gun to 25BAR, as the ball valve is rated to 50BAR, and I trust my soldering skills and am confident about that schrader.
This is a blury image of my soldering.

If your getting chased off a police dog, try not to run through a tunnel then onto a small see-saw then through a ring of fire. They are trained for that!