When this rare Giffard gas pistol is brought into the shop on Pawn Stars, Rick is baffled; so he calls in his guy. They made less than 500 of these guns, and expert Craig Gottlieb thinks there are probably only 100 left in existence. So what's so special about it? Typically, guns get their firing power from compressed air. This gun, however, uses carbonic acid (a liquid that, under normal temperature and pressure, would be a gas). When the trigger is pulled, a small amount of the liquid is released. It then expands into a gas and creates a tremendous amount of pressure!