Learn more about gearbox air compression in this video from AirsoftReviews HD... "In this technical video, we explain how a gearbox can lose fps rate cause to bad air sealing and low air compression due to technical problems. Using an upper receiver from a G&G L85A2, we will give you usefull advice of how you can increase air sealing only with some modification that will not cost you money. Stay tuned for more technical videos on AIRSOFT REVIEWS HD!"