The Modular Sniper Rifle, or MSR, is a bolt-action sniper rifle recently developed and produced by Remington Arms for the United States Army. It was introduced in 2009, and was designed to meet specific United States Army and USSOCOM Precision Sniper Rifle requirements. The MSR won the PSR competition, and is called the Remington Mk 21 Precision Sniper Rifle in U.S. military service.