From The Manufacturer/Wikipedia/People Smarter Than Us:
Our melonited corrosive resistant CrMoV (Chrome-Moly-Vanadium) 4150 barrels provides excellent coating uniformity and no tolerance build up in the barrel to create deviation. Our melonited barrels have higher lubricity, last longer and are just plain tougher than chrome lining. The barrel chambers are speed polished reducing resistance on the cartridge entering and exiting the chamber.