Squad Designated Marksman Rifle
The Squad Designated Marksman Rifle (SDM-R) is an American designated marksman rifle used by the United States Army. It is essentially a heavily modified M16 rifle designed to provide U.S. Army designated marksmen greater accuracy and firepower at longer ranges, increasing an infantry squad's effective range to up to 600 meters.
Source: Wikipedia — Squad Designated Marksman Rifle (CC BY-SA 4.0)