This 5.56 NATO chambered 16 inch Performance Series Barrel is machined from 4150 Chrome Moly Vanadium steel with a QPQ Corrosion Resistant Finish. Ballistic Advantage's Performance Series Barrels feature a Nickel Boron Coated Extended M4 Feed Ramp Extension. Hanson Series Barrels feature Ballistic Advantage's proprietary BA Hanson profile and include a pinned lo-pro gas block. Hanson barrels are not designed to work with aftermarket piston kits. The original BA Hanson profile barrels have a .750" diameter at the gas block journal and it is more of a light/medium contour. The BA Hanson .625" barrels are called this due to .625" diameter at the gas block journal. This profile is a thinner and lighter weight version of the original BA Hanson profile. Each BA Hanson barrel comes with a pinned, lo-pro Gas Block already installed which makes them an excellent value.