Well, I've been trying different types of high pressure burst discs lately. My gun stopped working as a hybrid, no idea why. I have my meter length and pressure set correctly according to SpudTool (AdvancedSpuds) and FuelTool (BurntLatke). It's all steel, so I've been shooting it at ridiculous pressures as a pneumatic. I used two layers of aluminum soda can today, as a burst disc. They held
350 psi! I couldn't pump further with my bike pump (I was literally jumping on it), so I waited. After a minute or two, the thing went off, totally randomly. The steel ball bearing went through 6 soda cans, two layers of 1/2" plywood (the backstop

), through my tin shed, out the other side, and finally left a 1/2" deep dent in my 3/4" plywood fence. It was extremely loud, louder than anything I've ever heard. Usually the gun sounds like a rifle, but this shot was louder than a shotgun. I can barely hear now.
Give me your opinion, was it supersonic or not.
Almost forgot, this gun's barrel is 10 feet of 1/2" PVC for those who don't know.