The Sig Sauer Sig 556 Sportsman Configuration Model is a semi-automatic tactical carbine chambered in 5.56 NATO. The SCM differs slightly from the standard model with features such as a fixed synthetic stock and a crowned muzzle. Otherwise it has a cold hammer forged barrel, so a machine carefully cut the grooves in the bore. This process produces very durable rifling. The SCM has a Picatinny rail that runs along the top and bottom for easy mounting of accessories and optics.
The SCM is gas operated instead of gas piston operated, so the propellant gases flow through a tube aimed at a tube in the bolt. The gas pushes the bolt rearward in turn cycling the action.
Sig Sauer recommends the SCM for leisure or sport shooting.