High-Quality, Realistic M4A1 GBB Rifle within the Legal Limits Meets the Highest Expectations for the Passionate Airsoft with Viper Techs Tailored, End User Performance Specific GBB Rifle Crisp, Short Wall Break, Two-Stage Trigger System Short Stroked CNC Steel Bolt and Nozzle Design 18mm Aluminum Nozzle Head for Sharper Recoil Impulse, at cost of compatibility with CO2 Magazines Real Steel Spec. Configuration; 14.5-in Outer Barrel with 1/2"x28 Threading 1-1/4-incx18 TPI Handguard Ring RS Mil-Spec 1.146-inch or 29mm Buffer Tube Threading 6.04 375mm Viper Tech Brass Inner Barrel CNC KAC M4 Style RAS Handguard GHK WA WOC System, Hop Adjustment found beneath Outer Barrel 6 Position Buffer Tube with Crane Stock Smooth, Grain-free Interaction between Metal Components Deep Engraved Colt Licensing and Rollmarks CNC 6061-T6 Aluminum Forged Receiver with Phosphate Treated CNC Steel Components Hard Anodised Matte Black Finish This product is only compatible with gas designed specifically for Airsoft guns. Do not use lighter fluid or butane gas, as that will cause permanent damage.