Gas powered pistols are capable of semi-automatic firing. The nonblowback Airsoft pistols tend to be a bit more powerful than the blowback versions, due to the fact that all the gas is used to propel the BB’s, whereas blowback versions use some of the gas to operate the blowback mechanism of the pistol. Since all of the gas in the pistol is used to propel the BB’s, the magazine does not have to be refilled with gas as often as the blowback types of pistols. The non-blowback pistols are usually made of nylon/fibre or ABS, and can be found in versions with either fixed- or adjustable Hopup systems. Most of the popular models can be found as gas non-blowback Airsoft pistols.