Premium Grade AR-15 Barrel 16\" Contour, w/ 1:10 TWIST 9mm, Nitride finish This AR-15 16\" Government Profile Nitride 9mm barrel has a blowback gas system with a 1:10 twist. Our AR-9 parkerized rifle barrels are made from the finest 4150 Chrome Moly Vanadium and precisely rifled for high accuracy at a great price. All finished barrels go through a 100% inspection process. Inspections Equipment includes CMMs and Air Gauges for the bores as well as visual and machine inspection. Don\'t forget the AeroShell 33MS Mil Spec Armorer\'s Grease!