The reciever could get a signal that looks like the actual signal, and set off the ignition. Wires are cheaper and more reliable, ableit less cool, but we cant have everything.

It might slow the shrapnel down, but i dont think it would be worth trying. If a chamber bursts and you are near it, you will be hurt no matter what you do.

Any sonic boom would be covered up by the explosion in the combustion chamber. An example is a .22 bullet-it goes past the speed of sound, but no sonic boom.

I did some basic chemistry to get those figures (PV=nRT). However, those calculations did not include the effect of detonation or efficiency, and that probably changes everything.

I did some calulations, and if you started with a 70 psi Nos-Propane mix, the final pressure would be close to 1000 psi. It would also be about 3000 degrees F. Plastic will not hold that kind of pressure (or temp), but metal will.