DoubleStar 16in 1x9 DS-4 Gov't Barrel with Forged Sight Base Black. 9 twist. w/Forged sight base Features of Doublestar 16in 1x9 DS-4 Gov't Barrel with Forged Sight Base BBL: DS4 16" Gov't Barrel Twist: 1.9 Sight Base: Forged Package Contents: Doublestar 16in 1x9 DS-4 Gov't Barrel with Forged Sight Base What firearm models does the manufacturer say DoubleStar 16in 1x9 DS-4 Gov't Barrel with Forged Sight Base is compatible with? The manufacturer says that DoubleStar 16in 1x9 DS-4 Gov't Barrel with Forged Sight Base is compatible with AR-15DS4 16 Gov't BBL 1.9 twist. w/Forged sight base Features/Specifications: BBL: DS4 16 Gov't BarrelTwist: 1.9Sight Base: Forged