Gas Airsoft are usually associated with pistols due to the insufficient room to store high-powered electric gear propulsion mechanisms. There are efficient gas powered rifles too. A feature included with many gas powered Airsoft is the ability to adjust velocity. This can come in handy when you're adjusting your gear to qualify for specific fps requirements. Most Airsoft gamers will carry a gas powered pistol as a side arm. Gas power is generally associated with guns that have "blowback" features. Blowback is when the propellant (gas) is used not only to send the BB on its way, but also to operate the slide of a gun to recreate the realistic firing cycle of a semi or fully automatic weapon. The common gases are Green Gas and HFC-134a. The less common options are CO2, nitrogen and red gas. Refer to your owner's manual to determine which gas options are suitable for your gun.
• Green Gas - Green Gas in made up of polysiloxane lubricant (silicone) and propane. It's smooth (consistent chamber pressure) and can withstand high temperature extremes. It is the gas of choice and works well in low temperatures. It's powerful and the user should ensure that their gun is capable of handling the power without causing damage. The silicone additive keeps the seal lubricated which prolongs seal life and minimizes the need for seal maintenance. A silicone additive to gases is a welcomed prevention solution.
• HFC-134a - This gas is often viewed as the most inferior gas option. It's consequently the cheapest gas on the market. It's extremely temperature sensitive. Lower temperature = less power or insufficient power to discharge your gun. This gas was used in air-conditioners and refrigerators. This is not a very high intensity propellant and that is good to know if you're choosing which gas to use in a gun that isn't designed to handle higher pressure gases. Guns rated for HFC-134a propellant ONLY may be destroyed by the use of other gas propellants.
• CO2 - CO2 is a liquid gas that is converted into a vapor when exposed to external air temperature. The subsequent chamber pressure propels the BB. Because of this liquid to vapor conversion, CO2 is a temperature sensitive gas option and will be affected by the ambient temperature of the shooting environment. However, you can purchase CO2 designed for particular temperature ranges (e.g. 39° - 64°F and 64° - 104°F) to lessen the pressure fluctuation associated with CO2.
• Nitrogen/High Pressure Air (HPA) - Nitrogen is immune to the effects of temperature extremes. Compressed air offers smoother shooting with substantially less velocity fluctuations. This is primarily due to the fact that compressed air is already a gas and no conversion needs to take place as with CO2. Therefore, the pressure stays relatively constant. Nitrogen is more expensive than CO2.
• Red Gas (Freon22) - Red Gas is one of the most powerful gases for Airsoft and it can increase your fps performance. Because of the red gas power, you get faster blowback action, which means an increase in ROF. Your gun may require modification to make it compatible with Red Gas. Otherwise, the high pressure may damage the internal mechanics of your gun. In order not to void your warranty and/or destroy your gun, know what the recommended gases are for your Airsoft equipment. Red Gas is sometimes difficult to find and will increase the maintenance factor, even on ABS constructed Airsoft.