At one point, before AEGs came around in the 1990s, all semi-automatic Airsoft guns were powered by gas. These generally had external tanks for the gas (like paintball guns), and worked quite well, but they weren’t very compact. Nowadays when you buy a gas Airsoft pistol you will most likely be buying a Gas Blowback. GBB guns are very popular as side arms, and before AEPs (Automatic Electric Pistols) came out a few years ago gas-powered guns were basically the only option for a semi-automatic Airsoft pistol. “Blowback” refers to the fact that the gun actually cycles the slide when firing, providing a much more realistic feel. Gas pistols exist that do not cycle the slide, called NBB (No Blowback) guns. These are more efficient than GBB guns because they operate essentially the same way but do not waste gas cycling the slide. They aren’t anywhere near as fun though. There is also an alternative to GBB called EBB, or Electric Blowback. These guns use a battery to cycle the slide. Unfortunately they don’t work very well. They don’t fire BBs at a high enough FPS. They also have slow firing rates and the action of the slide isn’t very realistic. They generally won’t be exact 1:1 scale replicas and are produced on the cheap. I would not recommend an EBB Airsoft gun.
GBB is generally used in handguns, although SMGs and even rifles exist. A lot of the crazier GBB guns are really complicated and don’t work that well, but there are many extremely solid GBB pistols available. There are a few drawbacks to GBB handguns and a couple advantages. The drawbacks include bad efficiency compared to battery-powered guns, performance being affected by weather, generally plastic bodies, lower accuracy at distance, and required knowledge of the different available gasses. The main advantage is that they are just a riot; it’s pretty much the closest you can get to shooting an actual firearm. Most of them can also be field stripped, or taken apart quickly without the need for tools.
Gas Blowback operation isn’t too complicated, there are actually less moving parts than in an AEG. They have hammers and slides and operate more like real steel firearms than AEGs as well. It all begins with filling up the mag with gas through the filling valve, and loading up. The hammer on GBB handguns is actually just cosmetic; the real hammer is inside the gun sitting underneath the cosmetic hammer. When the trigger is pulled the hammer strikes the firing valve, which is a valve located above where the gas is stored in liquid form. When the firing valve is struck it opens, allowing gas to rush up from the magazine into the cylinder. From the cylinder the gas continues to travel out the barrel, firing the BB. At the same time, pressure in the cylinder forces back the blowback ram. When the ram gets forced back, so does the slide. The slide is the top part of the gun that goes back and forward when you fire just like with a real steel pistol. When the slide moves back it cocks the hammer again, which in turn closes the firing valve and stops the flow of gas into the pistol. At this point a spring that is attached to the cylinder begins pulling it back into place. Without this spring the slide would just be loose and go wherever it wanted. As the slide returns to its starting position it grabs another BB from the top of the magazine and chambers the round. At this point the cycle is complete and another BB is ready to be fired. All this happens in a fraction of a second, and GBB guns can pretty much fire as fast as you can pull the trigger. Some are fully automatic as well, certain Glock models for example.
These are the inner workings of a GBB pistol. As you can see, the operation is not too far off from that of a real steel firearm. GBB guns provide an exciting change from springers or AEGs, and although they require more maintenance and are less efficient, the enjoyment you will get out of them is worth the cost. They make excellent side arms and are the most fun Airsoft guns to target shoot with. There are many high quality GBB Airsoft guns on the market, and there is sure to be a perfect one for you at HobbyTron.com. See you on the field.