The gas pistols of the category GBB (Gas Blow Back) have the so-called blow back function. With these models the slide repeats with every shot and the next BB is loaded automatically (semi-automatic). Some guns also have a full auto mode, that fact will be indicated in the product description. Gas weapons are particularly suitable for warmer environments (> 15°C) and for short to medium distances (<40m).
Most GBB guns have a plastic frame and grip on while the slide is often made of metal. These weapons contain the note "Full Metal" or "Metal" in the product name or product description. The mechanical part of the weapon should be maintained from time to time by taking off the slide and applying silicone oil. Oil products for genuine firearms should not be used because they contain substances which can harm the airsoft gun. Unless noted to the contrary in the product details all weapons are generally semi-automatic.
Guns are supplied without gas which must be purchased separately. In the category Gas & CO2 it is described which gas should be used for which gun.