The Heckler & Koch MR556 A4 is the latest civilian iteration of the legendary HK416 platform, chambered in 5.56x45mm NATO and configured as a factory short-barreled rifle with an 11-inch cold hammer-forged barrel. The MR556 A4's short-stroke gas piston operating system keeps hot carbon fouling out of the action, enabling the rifle to run longer with less maintenance and reduced wear on internal components compared to direct-impingement designs. An adjustable gas regulator allows the operator to tune the system for both suppressed and unsuppressed operation. The A4 generation brings full ambidextrous controls — including bolt catch/release, magazine release, and 45-degree selector levers with tactile fencing — along with a free-floating M-LOK handguard, a full-length Picatinny top rail, and a proprietary steel barrel nut that acts as a heat sink to minimize temperature buildup during sustained fire. The non-chrome-lined, cannon-grade hammer-forged barrel delivers exceptional accuracy and durability. As an NFA-regulated item, this SBR requires ATF Form 4 approval and a federal tax stamp prior to transfer. Heckler & Koch MR556 A4 5.56 x 45mm 1:7 Twist Threaded 11"Bbl Short Stroke Piston Adjustable Gas Black MLOK Short-Barreled Rifle w/ 10rnd Mag 81001049