Griffin Armament ATM (Advanced Threaded Match) Barrels are billet machined from 416R chromium stainless steel to exacting tolerances for the ultimate in drop in match performance. Chambers are honed and polished to ensure an extremely smooth surface finish and optimal reliability with a wide range of ammunition from training to duty ammo. Two years of research and testing provided the appropriate knowledge to machine the barrel dimensions for a perfect fitment; providing the best possible accuracy without sacrificing factory reliability.