Designed by Federal Ammunition to increase the maximum effective range of the AR-15 rifle platform, the .224 Valkyrie offers superior ballistic performance when compared to the traditional .223 Rem/5.56 NATO cartridge.Criterion Barrels Inc. is now offering select AR-15 barrels chambered in .224 Valkyrie. Hand lapped and manufactured from 416R Stainless Steel, these barrels are currently offered with a salt bath nitride finish or left "in the white". All models come standard with a 1-6.5 twist.Chambers are finished, but barrels should be headspaced and installed by a qualified gunsmith.