You can find the Ballistic Advantage Modern 18" 5.56 1:7 SPR Rifle Gas System Barrel here.

Ballistic Advantage Modern Series 18" 1:7 twist Barrel with a Rifle Length gas system, SPR barrel profile and chambered for 5.56 NATO.

Ballistic Advantage Modern Series barrels are machined from 4150 Chrome Moly Vanadium Steel and finished with a corrosion resistant QPQ Salt Bath Nitride treatment. The M4 feed ramp extension also has a QPQ finish.

Caliber 5.56 NATO
Barrel Length 18"
Twist Rate 1:7
Gas System Rifle Length
Barrel Profile SPR
Inside Finish Salt Bath Nitride
Outside Finish Salt Bath Nitride
Material 4150 Chrome Moly Vanadium
Muzzle Thread 1/2x28 TPI (Threads Per Inch)
Diameter At Gas Port .750"