Sturm, Ruger & Company, Inc. announced the availability of three, AR-style upper receiver assemblies featuring the innovative two-stage, piston driven performance of the SR-556 family. These rugged and reliable SR-556 piston driven uppers run cleaner, cooler, and are easier to maintain than traditional gas driven systems, offering significantly improved reliability.
Now all AR owners can enjoy the features of the SR-556 platform, including the two-stage piston driven operating system that provides a smooth power delivery stroke to the action and vents combustion residue out of the bottom of the gas block. The four-position adjustable gas regulator allows the operator to tune the rifle to specific ammunition and rifle conditions, minimizing recoil and maximizing reliability and long-term endurance. Reliability is further enhanced by a one-piece bolt carrier with an integral transfer key. Designed for long-lasting accuracy, the chrome lined barrels are cold hammer-forged from Mil-Spec 41V45 Chrome-Moly-Vanadium steel.
The standard SR-556 upper chambered in 5.56 mm NATO/.223 features a heavy contour, 16.1-inch barrel with a 1:9 twist rate, and is capped with a Mini-14/SR-556 flash suppressor mounted on 1/2-28 threads. A one-piece, ten-inch quad rail handguard provides ample room for mounting sights, optics and accessories. Made exclusively for Ruger, this SR-556-specific handguard is pinned to the upper receiver, creating a near-monolithic upper receiver assembly and providing a rugged mounting system for the piston driven transfer rod.
A carbine-length version of the popular SR-556 two-stage, piston driven AR-style upper is also available. The carbine upper features a heavy contour, fluted barrel that is 1 3/4 inches shorter and a half-pound lighter than the barrel on the standard SR-556. The 1:9 twist rate, 16.1-inch barrel on the carbine features an integrally machined flash suppressor, which minimizes the overall length of the barrel while complying with ATF regulations for civilian and commercial sales. This carbine version maintains the mid-length gas system and heavy (.850") barrel contour under the handguard, but the barrel is fluted for weight reduction and to promote barrel cooling.
Those seeking to equip their modern rifle with ample power for hunting medium-sized game or greater muzzle and downrange energy capability for defensive or tactical roles can select an upper chambered in the capable 6.8 SPC caliber. The SR-556/6.8 features upper features a heavy contour, 1:10 twist barrel with a standard SAAMI 6.8 SPC chambering. The chrome-lined, cold hammer-forged barrel is 16.12 inches long, is threaded 5/8-24, and is capped with the effective and distinctive Mini-14/SR-556 flash suppressor.
All three uppers are equipped with folding, back-up iron sights. These rugged, high-quality sights co-witness with Mil-Spec optics, and are easily removed or replaced. The sights can be folded down with the push of a button, or quickly flipped up with thumbs. The windage adjustable rear sight includes an instantly converted short and long-range aperture, and the protected front sight is elevation adjustable.
Durability and performance of the SR-556 is enhanced with the use of high-performance finishes: The barrel and gas block are chrome lined, while the piston, bolt, bolt carrier, and extractor are chrome plated. The piston driven transfer rod is electroless nickel/Teflon coated. The flash hider and the exterior of the barrel, gas block, and regulator are manganese phosphate coated. All aluminum parts are Mil-Spec hard coat anodized.
The SR-556 rifle and carbine uppers chambered in 5.56mm NATO are shipped with three, 30-round Magpul PMAG magazines. These lightweight magazines feature a storage/dust cover, a stainless steel spring, and a self-lubricating, anti-tilt follower. The 6.8 SPC chambered upper is shipped with one 5-round magazine and two 25-round magazines. Three rail covers, provided with each upper, provide a comfortable ergonomic hold when carrying or shooting.