Air Seal

From the piston head against the cylinder wall, to the nozzle against the chamber, to the hop-up chamber against the inner barrel, every joint the compressed air passes through is a potential leak point. A single worn O-ring or a nozzle sealing slightly off-centre can quietly cost significant FPS and, more importantly, shot-to-shot consistency.

Improving air seal — new O-rings, a better-fitted nozzle, a properly bedded hop-up chamber — is usually cheaper than any other upgrade and often delivers a bigger accuracy gain than a fancier inner barrel alone, which is why techs check it first when a gun underperforms its spring rating.

A simple diagnostic many technicians use is blocking the barrel tip and dry-firing once: a gun with good air seal resists noticeably, while one that fires easily with the barrel blocked is leaking somewhere in the chain.