Chrome-lined, button rifled barrels feature 223 Wylde chambers and 1-8" twist for enhanced accuracy potential with both .223 and 5.56 NATO ammunition. Unique chrome-lining process maintains uniformity throughout the bore and hand-lapping helps ensure smooth, consistent lands and grooves. Gas ports are optimized for barrel length and chambering to help ensure reliable cycling, and are available for carbine, mid-length, and rifle gas systems. Also features 1/2"-28 tpi muzzle threads for standard comps and flash hiders, plus M4 feed ramps on barrel extension to aid in smooth, reliable feeding. Barrels now feature a dimple opposite the gas port, so screw-on gas blocks do not shift during firing. Hybrid contour barrels have a reduced and tapered contour under the handguard to save weight. HBAR contour barrels feature .870" diameter under the handguard for rigidity and extra heat absorption.