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Rather than relying on the pressure caused by the combustion of a flammable powder, CO2 guns use compressed carbon dioxide to propel projectiles. CO2 guns typically fire steel balls, called “BBs,” or soft lead pellets. Popular among recreational shooters and small-game hunters, some CO2-powered weapons fire projectiles at more than 400 feet per second.
Compressed Carbon Dioxide
Manufacturers use carbon dioxide as a pressure source because of the unique properties of the compound. Once inside a pressurized container, some of the carbon dioxide transitions into the liquid state, leaving a container containing both a liquid and a gas. As the shooter pulls the trigger, it opens the valve on the cylinder, which lets some of the gas escape into the barrel. The sudden drop in pressure is explosive, and causes the projectile to fire out of the gun's barrel. Some of the liquid in the cylinder transitions into the gaseous state to replace the escaped gas, thereby preparing the cylinder for another shot. Because carbon dioxide cools as it expands, rapidly firing many shots in succession causes the gun to cool significantly.