Seems like I've seen this before. Maybe on one of the forums or whatever. Someone had made an airgun that used some sort of metal foil to hold back the pressure until finally, Kapow! Not a bad idea actually, except I've have to buy pellets AND burst discs:)
BTW, I work with the Airgun to end all airguns. Mine shoots about 3 tons at about 45mph, but the acceleration is at about 16g's from a dead stop!