I'm making a pnuematic potato cannon and I need help on what is the best piston release method?

I know of two ways, but am looking for advice from veterans. I am not a novice at this, and cost is not a problem, so give all and any ideas. (illogical ones are accepted!)

I've always used a ball valve on my potato cannon. You can open it up quick enough and it always works. The opening should be about as large as the barrel.

You could also use an solenoid valve (sprinkler valve). It opens faster, but you have to make sure that it operates at the desired presure. The opening should be big enough too.
Re-design6 years ago
Use a .5" disk of deldrin. encircle that with a plasma generator. Now on firing the plasma generator vaporizes the disk in 2 microseconds thereby releasing all of the pressure instantly. Or you could just use a big globe valve with a long handle.