The SIG 556 semi-automatic rifle is gas operated, using a short-stroke gas piston located above the barrel. The gas system has a manual gas regulator with two settings, either for normal or harsh conditions. The barrel is locked using a rotary bolt with two massive lugs. The receiver is redesigned from the original SIG SG 550 rifle, and features a stamped steel upper part mated to an aluminum alloy lower part. The lower houses a trigger unit and a redesigned magazine accepting all M16 / Ar-15 type magazines. A bolt stop device is incorporated into the design. The manual safety is ambidextrous and located above the pistol grip. Includes a Burris AR-536 5x 36mm Prism Sight and Magpul MBUS flip-up sights.

Caliber: 5.56 X 45mm NATO
Action Type: Semi-auto
Stock Style: Collapsible
Type: M4 Style
Overall Length: 37.0"
Length w/ Stock Collapsed: 33.5"
Barrel Length: 16” Cold Hammer-Forged
Flash Suppressor: A2 Style (.5x28TPI)
Rifling: 1 in 7"
Sight Radius: 21"
Forearm: Polymer
Weight w/o Mag.: 7.8 lbs
Operating System: Full Length Gas Piston Rotating Bolt
Magazine Capacity: 30 Rounds