NOTE: In order to quickly change the spring, follow these simple steps: 1) remove buffer tube; 2) using a 3mm Allen key, remove the retaining plate; 3) with a large Allen key, you can now remove the spring guide and spring to replace with your choice of spring.Ammo type: Seamless 0.25g or heavier (0.25g, 0.26g, 0.28g, 0.30g, etc) BBs. For maximum performance and accuracy, Airsoft Megastore recommends Lancer Tactical BBs, which carry perfect spherical consistency and density, available at Airsoft Megastore.In the Box1X Rifle1X MagazineSpecifications:Brand: Classic ArmyOperation: Electric AutomaticBuild: Metal Receivers, Outer Barrel / Polymer Stock, Motor GripFiring Modes: Full-Automatic, Semi-Automatic, Programmable Burst, SafetyMuzzle Velocity: 390 - 400 FPS (w/ 0.20g BBs)Gearbox: Full Metal Version 2 (w/ 9mm Bushings)Connector: Small TamiyaBattery: 7.4V Buffer Tube LiPo (not included)Magazine Capacity: 300 Rounds (High Capacity)Hop-Up: AdjustableInner Barrel Diameter: 6.03 mmInner Barrel Length: 380 mmWeight: 7 lbsColor: GrayCalifornia Proposition 65 Warning: Cancer and Reproductive Harm - www.P65Warnings.ca.gov