This is a Ballistic Advantage Barrel known as the Modern chambered in 308 Winchester, model BABL308007M.
This .308 chambered (DPMS style) 18 inch Heavy Profile Modern Series Barrel is machined from 4150 Chrome Moly Vanadium steel with a QPQ Corrosion Resistant Finish and QPQ coated M4 feed ramp extension.
Features:
4150 Chrome moly vanadium
Heavy profile
QPQ finish
Rifle-length gas system
1:10 twist