LWRC's ICDI Upper Receiver is a perfect start to a custom AR build. It utilizes LWRC's direct impingement operating system with a keyless bolt carrier design and proprietary DI bolt carrier group. The 16.1-inch barrel features button cut rifling and features unique spiral fluting. The barrel is topped with 1/2x28" threads for muzzle devices and suppressors. Other features include an ambidextrous sling mount, an ambidextrous charging handle, an H2 buffer, and a carbine length action spring. Features of the ICDI Upper Receiver: LWRCI DIRECT IMPINGEMENT SYSTEM LWRCI COLD HAMMERED BARREL LWRCI PROPRIETARY DI BOLT CARRIER GROUPLWRCI AMBIDEXTROUS SLING MOUNT LWRCI AMBIDEXTROUS CHARGING HANDLE H2 BUFFER CARBINE LENGTH ACTION SPRING LWRC International LWRC ICDI Direct Impingement .300 Blackout 16.1" 1:7" 5/8x24 Bbl Black Complete Upper Receiver ICDIU3B16