Although the use of CO2 as a propellant gas began in France, Crosman pioneered its use in the U.S. almost 60 years ago. The advantage of using CO2 to drive projectiles lies in the fact that a small container of liquefied gas can be held within the gun and provide power for a large number of shots without any pumping. Crosman developed the Powerlet which holds 12gms of CO2 and is the standard for the industry. Carbon dioxide is a convenient gas to use in airguns (although they strictly do not fire by air pressure, guns that are powered by CO2 are still referred to as air guns). It is inexpensive, nontoxic and noncorrosive. Another desirable feature of CO2 is that the liquid exerts a vapor pressure that can be as much as 700-800 lb/in2 at temperatures of 70-75-Degree F. A pressure this high is sufficient to propel a 0.177 caliber pellet at velocities approaching 700-Feet per second or a 0.22 caliber pellet at almost 600-Feet per second. Therefore, it is possible to produce rifles powered by CO2 that are versatile enough for most airgun uses. The widest use of CO2 is in pistols. A CO2 Powerlet is compact enough to fit in the grip of the pistol which allows a magazine to hold several pellets and several shots to be fired without reloading or recharging a reservoir. The result is that pistols can be made to resemble specific firearms very closely which provides an element of realism. Other pistols provide for attaching the Powerlet in a tube below the barrel and operate as bolt actions. The major disadvantage of CO2 as a power source is that the vapor pressure it generates is dependent on the temperature. On cold days, the pressure is lower which results in pellet velocity being lower. As a result, CO2 guns are more practical in situations where the ambient temperature is above 60-Degree F. There are times when the number of shots provided may not be adequate for the sport. Crosman responded with the AirSource, a larger cylinder that holds 88gms of CO2. This much CO2 provides enough propellant for as many as 300 shots. Crosman adapted the Model 2250 compact rifle and the Benjamin 392 to utilize the AirSource tanks, as does a special version of the Model 1077.