The Heckler & Koch MR556 A4 14.5" Upper Receiver Kit is a high-performance, short-stroke gas piston conversion system engineered to bring military-proven HK416 reliability to the standard AR-15 lower receiver platform. This complete package is centered around an exceptional 14.5-inch cold-hammer-forged barrel that ensures superb accuracy, a longer service life, and robust performance under extreme conditions. The system utilizes a unique pushrod gas mechanism that prevents carbon fouling and hot gasses from entering the bolt carrier group and receiver cavity, maximizing cycling consistency while running cleaner and cooler. It features a user-adjustable gas regulator specifically optimized for seamless transitions between suppressed and unsuppressed shooting configurations. Outfitted with an extended ambidextrous charging handle, a slim-profile free-floating M-LOK handguard, a tungsten-filled buffer, and a buffer spring, this comprehensive kit arrives ready to immediately upgrade your rifle build. Heckler & Koch Upper Receiver Kit for MR556 A4 w/ 14.5" Barrel & MLOK Handguard 51001918