How to reinforce pvc pipe for potato cannon?

Consider secondary containment. My current cannon (about to be retired) is constructed using 3" ABS for the combustion chamber and 1.5" ABS for the barrel. I'm using 4" ABS as a 'blast shield' for the chamber and 2" ABS for a blast shield covering the barrel. It's a little difficult to describe concisely, but I can email you a digital photo. My current prototype uses pressure-rated schedule 40 PVC for the combustion chamber and barrel, along with the ABS 'blast shields'.