An AR-15-style assault rifle made by Heckler & Koch. Looks a lot like the M4 carbine but has a railed forearm with folding front sight and internal changes. It can be outfitted with a variety of barrels, ranging from 228-505mm (9-19.9 inches) in length.
See also
H&K HK417 (larger caliber variant chambered for 7.62x51mm NATO)
