FN America Barrel Ar-15 Button Rifled 16'' 17 Carbine Length Gas M4. This Rifle Barrel from FN America is made using incredibly durable materials that ensure a long lasting and efficient product. For a great way to make sure you are working with the best barrel that the shooting industry has to offer choose the FN America Barrel Ar-15 Button Rifled 16" 1:7 Carbine Length Gas M4. Specifications for FN America Barrel Ar-15 Button Rifled 16" 1:7 Carbine Length Gas M4: Manufacturer: FN America Color: Black Caliber: .223 Remington Barrel Length: 16 in Additional Features: Threaded Package Contents: FN America Barrel Ar-15 Button Rifled 16" 1:7 Carbine Length Gas M4