FN America AR-15 Hammer Forged 18 Inch Barrel Rifle Length Gas System 5.56mm NATO. 56mm NATO 36423 is the perfect way to improve your rifle by adding an excellent rifling piece. Made from a proprietary Chrome Moly Vanadium (CMV) steel the FN America AR15 Chamber Rod is hammer forged for greater strength and durability. Next barrels are air gauged and MP tested to make sure the barrel is free of microstresses and cracks. Finally barrels are chamfered deburred and cryogenically treated to ensure superior performance and accuracy. Using a .750 inch diameter gas block the FN America AR15 Hammer Forged 18in Barrel w/ RLGS 1/2 x 28 threading and has a right hand twist rate. For a great way to make sure you have a top of the line barrel on your weapon choose the FN America AR15 Hammer Forged 18in Barrel w/ RLGS 5.56mm NATO. Specifications for FNH USA AR-15 Hammer Forged 18 Inch Barrel Rifle Length Gas System 5.56mm NATO 36423: Mfg Item Num: 36423 Type: BARRELS - RIFLE Barrel Length: 18 Caliber: 5.56mm NATO Caliber-Gauge: .223 REM. Model Header: Rifle Length Gas System Master Model Header: AR-15 Hammer Forged Barrels The FN America AR-15 Hammer Forged 18 Inch Barrel Rifle Length Gas System 5.56mm NATO 36423 is a quality addition to the FN America lineup. For more great deals on AR15 Barrels by FN America please browse our FNH USA Gun Parts page.