Our 12.5" upper features a 1:7 twist rate, QPQ nitride finished barrel. Made from 41V50 chrome-moly steel, and is dimpled for gas block. We recommend using red locktite on the gas block screws before final assembly. We are using Ballistic Advantage barrels for these. Our M4 ramped uppers have a type 3 hard coat and machined from 7075-T6 forged aluminum.