Airsoft gas guns usually use one of three types of gas: CO2, a refrigerant known as HFC134a or what is known as "green gas." In these guns the gas is pressurized, which cocks the spring and prepares the gun for fire. Typically, Airsoft gas guns are pistols. These designs use small gas capsules, or reservoirs, that traditionally hide inside the handle. The majority of Airsoft gas guns offer semi-auto and full-auto modes.

What is green gas? Typically made from a mixture of propane and silicone oil, green gas is one of the most commonly used and most powerful propellants used with Airsoft gas guns. Although gun owners may be tempted to use green gas in their weapons, they should be aware that the gas might cause internal damage to a gun that is not designed to use it.

In order for an Airsoft gas gun to be capable of shooting in semi-auto and full-auto, it needs to be designed with what is known as a "blowback" function. Blowback is what occurs when the same gas used to project the BB "blows back" and pushes the slide back into place. This allows for a shot to take place every time the trigger is pressed, or repeated shots in a row if the trigger is held down.

A popular Airsoft gas blowback gun is the HG-185 pistol by HFC. This high quality 1:1 replica offers an excellent balance of efficiency and price. Its rubberized grip allows shooters to maintain good control over the weapon, while the full-metal magazine adds some weight for additional realism. With a velocity of 300 feet per second, it delivers excellent power for its compact size.