The SIG 556 is the US-market semi-automatic version of the SG 556/SG 550 family, produced in the US with Swiss-designed components. It features the distinctive polymer thumbhole stock, transparent magazines of the SG 550, and the gas-operated rotating bolt system. Discontinued when SIG shifted focus to the MCX and MPX families. Type: Rifle Action: Semi-Automatic Caliber: 5.56x45mm Capacity: 30 Year introduced: 2006, Switzerland Weight: 124.8 oz Overall length: 35.8" Status: Discontinued Intended use: civilian