This Gorilla Machining AR-15 20" heavy Mag Phosphate 6.5 Grendel barrel has a rifle length gas system with a 1:8 twist. Our 6.5 Grendel Mag Phosphate rifle barrels are made from the finest 4150 Chrome Moly Vanadium and precisely rifled for high accuracy at a great price. We recommend Defender 107 gr., Federal Gold Medal Berger 130gr.