FN SCAR 17S 20" barrel Assembly. The FN SCAR barrel assemblies are cold-hammer forged steel barrels with front sight assembly, gas block assembly, gas regulator, gas piston and flash hider installed. Assemblies can be easily installed by the user with a torque wrench and are ready to shoot without headspacing. This barrel will only fit FN SCAR 17 rifles chambered in 7.62 NATO. This barrel features a 1:12 twist rate.