Airsoft Gas Guns
The Most Popular Gas Airsoft Guns
The most popular airsoft gas guns are pistol airsoft guns. Airsoft submachine guns and airsoft sniper rifle guns commonly use gas airsoft guns mechanism. Like pistol airsoft guns, airsoft submachine guns typically feature a blowback mechanism. 
Sniper airsoft rifle guns omit the blowback mechanism to reduce recoil and increased muzzle velocities.
Some features that airsoft gas guns are favored are adjustable velocities or blowback feature. A blowback feature is a mechanism which cycles a slide or bolt to better simulate a real firearm's operation. Airsoft gas guns have mechanical complexities involved with distributing and regulating gas. Because of that reason airsoft gas guns have largely given way to electric airsoft guns for less specialized applications. However, airsoft gas guns still favorable for airsofters.
Airsoft gas guns mechanism is applied for use in replica grenades also. Airsoft Grenades fired from a grenade launcher such as the M203 or GP-25, or throwable grenades. These airsoft grenades both are projectiles with pellets, a rubber or soft foam head is seated in or on top of the shell. When the pressure is released the projectiles are shot from the launcher sent downrange. Inside the airsoft grenades there is a similar piston to the one used in the shells, but is on a literal timer that allows the user to clear the area of effect. Airsoft throwable grenades use pellets or powder as projectiles. Both type of airsoft grenades are not favored by airsofters because airsoft grenade launchers are expensive and the airsoft throwable grenades are not reliable.
Choosing the Right Gas for Your Gas Airsoft Gun
Airsoft gas guns become popular because of the realism, accuracy, operating action, and cost of operation. The most important thins in maintaining and the usage of airsoft gas guns is selection the appropriate gas. Choosing a wrong gas could damage the airsoft gas guns and harm the airsofter. The most commonly gas which is used by airsofter are 134A, green gas and CO2.
There are several factors when choosing the right gas for your airsoft gas guns. Airsoft gas guns are typically design for one type of gas. But there is a problem using one type of gas. The gas pressure as the power of airsoft gas guns depend on temperature. Decrease in temperature, the gas pressure inside the airsoft gas guns drop to a level there is not enough power to firing the pellets. This reduced pressure make the valve or airsoft gas guns remain open after shot and make remaining gas expulsion.
134A Gas
Gas selection should follow the manufacture recommendation. Airsoft gas guns manufacture in Japanese typically recommend 134A gas for airsoft gas guns with exceptions. 134A gas can be used under all but the coldest environmental conditions. When airsoft gas guns begin to misfire, it is safe to change the 134A gas to more powerful gas, such as green gas or propane.
Green Gas
Green gas is the post popular gas for airsoft gas guns, especially from other country than Japan. Green gas for airsoft gas guns is suitable for high ambient 
temperature. But in high temperature make green gas more powerful and could damage airsoft gas guns. If ambient the temperature reach to 100 degrees Fahrenheit you should switch to the less powerful gas, 134A, for you airsoft gas guns. The frequency of use airsoft gas guns should be considered as well. Airsoft gas guns use continuously, the process of expelling a little gas for each shot will lower the temperature of your airsoft gas guns.
CO2 Gas
CO2 gas airsoft guns will only able to accept CO2 gas. CO2 operates in a wider temperature range. CO2 airsoft gas guns are not favor airsoft gas guns because cost of operation and over all hassle of dealing with intricacies of this gas. Only some airsoft rifles specialties favor this CO2 airsoft gas guns.