The piston compresses the air that fires the BB. Get the piston right and the rifle shoots consistently. Get it wrong and every other upgrade is wasted effort.

Inside every AEG gearbox is a piston that travels back and forth, compressing air on the forward stroke and pushing the BB out of the inner barrel. Each shot stresses the piston between the rear gear teeth (which pull the piston back against the spring) and the front piston head (which compresses against the cylinder wall). Two factors determine piston quality: the teeth's resistance to gear strip damage, and the piston head's airseal against the cylinder wall.

Tooth construction is the first decision. Full-metal-tooth pistons have all 14 (or however many) teeth made of metal — maximum durability, handles heavy springs and high gear loads, but heavier (slower acceleration) and more aggressive on the sector gear. Hybrid pistons have metal teeth where stress is highest (last 4-5 teeth) and polymer teeth elsewhere — lighter than full-metal, durable enough for most loads. All-polymer pistons are the legacy and budget standard — light and cheap but strip teeth under heavy spring loads. Pick based on your spring: M90-M120 polymer is fine; M130+ needs hybrid or full-metal.

Piston head is the rubber-O-ring or polymer disc on the front of the piston that creates the airseal. Ported piston heads have small vent holes that reduce vacuum drag on the rear stroke — smoother cycling, slightly faster ROF, but require well-shimmed gearboxes. Non-ported heads are more forgiving of gearbox issues. Aluminum piston heads (SHS, Lonex CNC) seal better than polymer for ROF and consistency. For the cylinders the piston cycles in, see the dedicated collection.

💡 Titan Forge tip: If you're losing FPS on a recently-built gearbox, check the piston-to-cylinder airseal before suspecting the spring. A piston head O-ring that's worn or slightly under-sized can lose 30-50 FPS even when everything else looks fine. £8 of new O-rings can save a full rebuild.