GBB gun is most common type of airsoft which using compressed air to propel the pellet. The mechanisms of these gun using pneumatic potential energy from the compressed air, therefore the design is totally different as compare with spring and AEG powered airsoft. These guns use an internal canister that will releases the prefilled bottled gas upon trigger pull via a series of valves to propel the pellet. The guns are able for automatic and semi automatic due to the cyclically reload after a shot.
THe most common gases used are green gas and propane for GBB gun .Gas power tends to be used in airsoft pistols where size constraints make electric-powered mechanisms impractical. Other instances where gas is favored are where adjustable velocities are required or where a blowback feature is desired. A blowback feature is a mechanism which cycles a slide or bolt to better simulate a real firearm’s operation. Because of the mechanical complexities involved with distributing and regulating gas, these guns have largely given way to electric guns for less specialized applications, however, they still remain favorable amongst most airsofters. They are not just limited to pistols; submachine guns, sniper rifles and assault rifles commonly use gas mechanisms. Whilst the submachine gun replicas typically feature a blowback mechanism similar to the pistol replicas, sniper rifle replicas usually omit the blowback mechanism in favor of reduced recoil and increased muzzle velocity.