Ruger SR-556

The SR-556 is a semi-automatic rifle carbine manufactured by U.S. firearms company Sturm, Ruger & Company, Inc. The rifle was introduced in 2009, marking Ruger's entry into the popular AR-15 market. It is one of several new AR-15 platform rifles to utilize gas piston operation.

Overview
The rifle features a patent-pending, "two stage" piston mechanism as opposed to the standard AR-15 direct impingement system. Gas flow is controlled by a four position regulator. Several key parts, such as the short stroke gas piston, gas regulator, and bolt/carrier group are chrome plated. The bolt carrier features an integral lug in place of the AR-15's gas key. The flash hider is similar to Ruger's AC-556 and Mini-14GB.

The rifle includes a number of other manufacturer's parts such as a Troy Industries railed handguard and Samson folding iron sights, a Hogue rubberized pistol grip, and three Magpul PMAG 30-round magazines. The SR-556SC comes with three 10 round magazines and does not have the flash hider or collapsible stock, making it compliant in several states with restrictive assault rifle laws. The barrel is 16.12 in, chrome lined, and features a six groove, right hand, 1:9 in twist.

In August 2010, Ruger announced that the rifle would be offered in the 6.8mm Remington SPC cartridge.

Criticism
Ruger's introduction of the SR-556 was met with some criticism for its high price tag (US$2,000) and its weight. Ruger addressed these shortcomings by introducing a lighter and less expensive rifle, the SR-556E.