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 d Mfg: Criterion Barrels Inc SPECS: Length - 16, 18, or 20 inch. Profile - Hybrid or HBAR (18" & 20" only). Gas system - Carbine or Mid-Length (16"). Rifle (18" & 20"). Chamber - 223 Wylde. Finish - Parkerized. Chrome lined. Construction - 4150 Chrome Moly Steel. Hand L