Blowback

Whether the pressure comes from gas expansion (GBB/GBBR) or an electric piston stroke on some AEGs, blowback describes the same mechanical event: part of each shot's energy is diverted to shove a slide or bolt rearward, which a return spring then sends forward again, resetting the hammer or striker.

Beyond the felt recoil, working blowback usually enables features that a fixed-slide gun can't offer: a bolt catch that locks open on an empty magazine, a visible last-round indicator, and — on some designs — a slightly more realistic reload sequence. The mechanical complexity it adds is also the main source of GBB reliability issues in cold weather.

Some players deliberately choose a non-blowback gun specifically to avoid the felt kick, since a jumping sight picture between shots costs a fraction of a second of re-aim time that pure accuracy-focused shooters would rather not spend.