The Sig Sauer Sig 556 Classic is a semi-automatic tactical carbine chambered in 5.56 NATO. The Classic is the standard 556 model, which is a modified version of the Sig SG 550/551, a popular assault rifle used by US and allied forces. The biggest difference between the two, the 556 is only semi-auto.
The Classic has a gas piston operating system, which functions by propellant gases entering a port near the muzzle, the gas enters a tube that’s directed onto a piston and the piston connects with the bolt and pushes it rearward.
The Classic’s features include a cold hammer forged barrel, so a machine carefully cut the grooves in the bore. This process provides durable rifling. The Classic’s stock is collapsible for storage, but also adjustable for length. It has a polymer fore-end with a short Picatinny rail running along the top and bottom for easy mounting of optics or accessories. It has a rotary diopter rear sight, which provides four sight stations: CQB, 100m, 200m and 300m. It is also adjustable for elevation and windage.
Sig Sauer recommends the Classic for law enforcement and responsible civilians.