I'd just like to say, to anyone reading this that might be considering building a hybrid:
DO NOT USE A PVC BARREL If that barrel had been PVC, we'd have all had shrapnel wounds, possibly permanent damage. The energy of the failure was quite impressive.
I don't think I'll be getting a metal barrel though. It is extremely impractical to use a launcher this long unless you have a range in your back yard. Otherwise, it's just too unwieldy to be worthwhile. Right now I'm working on a way to get satisfactory power with a 6' or shorter barrel, which probably means using higher mixes. Which means spending more money. Which I seem to be running short of lately.
So the current idea is to make a 6' long, reinforced ABS barrel (1.5" inside 2" with fiberglass filling the space in between), and use it as a handheld

I would still have more muzzle energy than the biggest version of the SCTBDC, and slowly turning the steel plate into something with the consistency of swiss cheese with it shouldn't be too difficult.
But I still have the SCH 80 4" steel pipe, and it WILL be the meanest hybrid in the land by the end of the summer. Guaranteed.
Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.