The Valken Airsoft AEG Upgrade Spring is an internal gearbox spare part. This M130 AEG spring is made out of high quality wire with tension carefully measured. The FPS estimate is based on the average power output, and exact FPS result may vary based on alignment, installation, inner barrel, cylinder, and other factors. This airsoft main spring is rated for approx. 420-500 FPS. This AEG spring reduces stress, wear and tear for your gearbox.