Forgive me whats a QEV? It's probably getting late to have parts delivered befor Christmas but can I get any thing similar?

The ball valve is just what I have about but I can increase the siz of the valve and barrel or decease the size to help performance?

Hi, total new to this but seen a guy making a cannon on another forum and though this would be a bit of fun over the hoildays. Just really copying his simple design but now I'm wondering have a made a error at the start.

Sorry no pics but here is the basic idea. I made a metal tank today with a ...