The SIG556 is a semi-automatic rifle derived from the Swiss Army's Sturmgewehr 90 (SG 550/551), imported and sold in the American civilian market. A long-stroke piston operating system, folding polymer stock, and standard AR-15 magazine compatibility distinguished it from both the AR-15 and the AK-derived competition. The SIG556 was expensive and the folding stock was initially neutered for import compliance, limiting its appeal. Type: Rifle Action: Semi-Automatic Caliber: 5.56x45mm NATO Capacity: 30 Year introduced: 2006, Switzerland Weight: 7.8 oz Overall length: 36.5" Status: Discontinued Intended use: patrol, hunting, collector