Our chrome lined barrels are cold hammered forged and made with the material callouts and manufacturing process for the M249 Machine Gun barrel.The cold hammer forging process work hardens the steel around a rifled mandrel, which creates the lands and grooves. The barrel is then chrome lined to the spec for a M249 Machine Gun barrel, which is about twice as thick as that of an M4 barrel. The end result is a rifle that can be run hard day after day. For any high round count, high temperature, heavy shooting, we recommend our chrome lined barrel.