AEG (Automatic Electric Gun)

A rechargeable battery spins a motor, the motor winds a spring-loaded piston through a gear train, and releasing the piston fires one shot of compressed air down the barrel. That cycle repeats as fast as the trigger allows, which is what makes semi- and full-auto fire possible without touching a slide or bolt by hand.

AEGs dominate because the platform is cheap to maintain, tunable from stock to competition-grade internals, and forgiving of weather that stops gas guns cold. Nearly every rifle silhouette — DMR, LMG, CQB carbine — exists as an AEG first. The trade-off is recoil-free operation and a gearbox that needs occasional shimming and lubrication to stay reliable.

A used AEG is worth test-firing before buying: listen for a smooth, even cycle rather than grinding or a stutter, since a rebuild costs more than the gun itself sometimes did.