We are using 18 inch 1/8 twist made of 416 Stainless steel. The barrel is a 416 SS 1/8. It is chambered in .223 Wylde which is safe to fire 5.56 NATO from unlike .223 Remington. This has a F-Marked A2 front sight and flash hider. The Upper receiver is Mil-Spec with M4 feed ramps. BCG and charging handle are not included.