Pnuematics aren't really th same kind of shock that an explosive would be, but I'd still wrap the thing in burlap or hardware cloth... spiral wire isn't all THAT good at containing fragments..
ABS is probably _worse_ (more brittle) than PVC in this respect. There's very little pressurized use of ABS. The only one I can think of is Hypertek rocket motor reloads, but that's single-use, and wall thickness starts out at thicker than sched 160, hopefully the motor stops before it gets to sched 20 ;-) [+]
I'd prefer HDPE or schedule 40 or 80 PVC. But I don't think he can find anything with that ID in sched 40 or 80.
[+] Fuel grain is custom-molded ABS "pipe-like-thingie" with a nozzle on the business end. ABS because it's easy to get molded, and works better as fuel than PVC. HDPE is even better for that...
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