This is what 2A Armament says:
 
Building on our experience with lightweight firearms, 2A Armament set out to design a custom contoured 18" lightweight (31.5 oz) .308 barrel.  This barrel will ship as standard with our Xanthos rifle but is also available for individual purchase.

Features:

    4150 Barrel steel with QPQ Nitride
    .308 Caliber WIN MATCH
    Length 18"
    Rifle-length gas system .081 gas port
    1:10 twist, 5R rifling
    5/8-24 muzzle thread (.625 thread length)
    .750" diameter x 1.0” long gas block journal
    11 deg target crown
    LR-308 (DPMS Compatible) extension
    Weight - 1 lb 15.5 oz