13.7" Infidel 5.56mm Stainless Barrel --1 in 7" twist improved polygonal rifling --Extended feed ramps --Bead blasted finish --Mid length gas system --Gas tube --Pinned Low Profile Gas Block --1/2x28 threads --Medium Contour Weight: 30oz The barrel ships with gas block installed. This barrel is designed for our gas block that is 1" long(INCLUDED). A standard front sight base is 1.9" long and WILL NOT FIT. Barrel installation should be performed by a qualified gunsmith. Installation of the gas block dowel pin and gas block is required to complete the assembly process. All NFA Regulations apply. Please check your local and state laws before ordering. Contact your local ATF Field Office with any NFA questions you may have.