Ping Pong Vacuum Cannon

The velocity inside the barrel is 185MPH, then slows down to 136MPH once the ball leaves the frame.
I need to experiment with other burst materials. I'm currently using aluminum foil, but once I get to about 25 Hg, the foil can spontaneously break. So this cannon would be much faster if I could get around 28-29 Hg, but I need to figure out a better burst material.