Made from a strong mil-spec steel with black manganese phosphate finishing, this 16 button rifled FN America barrel is a great choice for any carbine length AR-15 rifle. Chambered in .223 Rem / 5.56x45mm, this chrome lined chamber with an M4 styled feed ramp will provide more consistent and reliable feeding while shooting. This barrel also features a 1/2 x 28 threaded muzzle and a 1:7 RH twist rate.