Once installed, the patented MCR upper receiver system can be user-configured in seconds without tools to adapt to virtually any mission profile. Specifically designed for responsible armed citizens, law enforcement and professional security personnel who wish to upgrade their rifle or carbine to MCR performance and capability standard features include gas-piston operation for extreme reliability in adverse conditions a 16.25″ quick-change (3 seconds) barrel system and a M-LOK co-planar hand-guard with rail-interface system for the mounting of optics and modern accessories. Spanning the capability range from the optic ready carbine through a lightweight support rifle the MCR accepts standard box type AR15/M16 magazines or M27 linked ammunition at operator discretion, permitting unprecedented firepower and weapon flexibility. KEY FEATURES Drop-On (MIL-Spec) Upper Receiver Assembly that upgrades your AR15/M16/M4 type lower receivers or rifles 5.56 x 45mm NATO 16.25” Quick-Change Barrel 1:7” RHT, ½”-28 TPI  Short-Stroke Gas Piston Operation Dual-Feed™ – Accepts ALL AR15/M16 Magazines & M27 Linked Ammunition Precision Machined 7075-T6 Billet Upper Receiver, Feed Cover and Charging Handle Precision Machined Billet Steel Feed Tray  Finish – Manganese Phosphate & Type III, Class 2 Hardcoat anodize – Black for Maximum Corrosion and Wear Resistance Dry Film Lubricant Applied to Critical High-Friction Surfaces Full-Auto Bolt Carrier  Handguard Style – M-LOK®  Adjustable Sight Set Quick-Change Barrel Handle Ships with Belt-Feed Main Action Spring, MIL-Spec H3 Buffer, Carbine Stock Spacer, Extended Bolt Catch, Mag Adapter, RipBrake Muzzle Compensator, (100) M27 Links & Operator’s Manual