Caliber 9x19mm - Operating system Roller- delayed Blowback Proven reliable - Semi Auto Action but is NFA Sear pack ready - Barrel 8.86 3 Lug Threaded Barrel 1/2x28 Nitride Treated for long life - Twist Rate 1/10 - Length 17.6 - Weight 5.05lbs - Trigger Pull 9-10 Lbs - Handguard Aluminum M-lok - Picatinny Optic Rail - End Cap Black Polymer with Sling Swivel - Original Paddle Style and Push Button Mag Release - Magazine 30 Round accepts standard Milspec MP5 Magazine