The SIG Sauer P556 is a semi automatic pistol variant of the SIG 556 rifle platform, manufactured by SIG Sauer in Exeter, New Hampshire. The SIG 556 family is derived from the Swiss SIG 550 series of military rifles, adapting the proven Swiss short stroke gas piston operating system and rotating bolt into a platform that accepts standard AR-15/STANAG pattern magazines. The gas system uses a two position adjustable gas regulator located above the barrel, driving a short stroke piston that actuates a two lug rotating bolt. This design avoids routing combustion gases through the receiver, as occurs in direct impingement systems. The P556 condenses this system into a pistol length configuration with a 10-inch barrel, and is fitted with a ribbed polymer pistol grip and trigger guard assembly. The upper and lower receivers are constructed from aluminum alloy, and the pistol is configured with a polymer vented handguard.

This example is fitted with a SIG Sauer STS-081 red dot sight mounted on the top Picatinny rail. The muzzle is equipped with an AAC 18-tooth (18T) closed tine flash hider. The pistol is configured with the standard polymer vented handguard and ribbed polymer pistol grip. The top rail features an integral flip up rear sight, with a flip up front post affixed to the gas block. Accompanied by one Brownells 30-round magazine, no original box or accessories included.

Specifications

• Manufacturer: SIG Sauer
• Model: P556
• Caliber: 5.56x45mm NATO
• Action: Semi automatic
• Operating System: Short stroke gas piston, two lug rotating bolt
• Gas Regulator: Two position adjustable
• Barrel: 10 inches
• Receiver: Aluminum alloy upper and lower
• Handguard: Polymer, vented
• Grip: Ribbed polymer pistol grip
• Muzzle Device: AAC 18-tooth closed tine flash hider
• Sights: Flip up front and rear 
• Optic: SIG Sauer STS-081 mini red dot sight
• Magazine: One Brownells 30-round magazine