Ruger SR-556

The Ruger SR-556 is a semi-automatic rifle from Sturm, Ruger and Company of the United States, introduced in 2009 as the firm's first AR-15 style firearm. It follows the general layout of the Armalite AR-15 family that Eugene Stoner's design gave rise to, but replaces the original direct impingement system with a two-stage, chrome-plated, piston-driven gas system working a rotating bolt. Gas is vented through the bottom of the gas block to keep the bolt carrier clean, and the gas cylinder carries a four-position regulator. The rifle is chambered for .223 Remington and 5.56x45mm NATO, with a 6.8mm Remington SPC version announced later, and takes STANAG box magazines. A 16.1 inch cold hammer-forged, chrome-lined barrel and a six-position collapsing stock are standard, and the weight is about 7.9 pounds. Ruger marketed it to law enforcement and military buyers as well as civilians, in Standard, Carbine and E-Model families.