This Rosco?16 in 300 Blackout (300 BLK) Barrel is perfectly suited for precision carbine shooters that plan on running only supersonic ammo, or are building a well-balanced hunting platform. Barrel Length: 16 inches Barrel material: 416r Stainless Barrel caliber: .223 Wylde Heavy profile Twist Rate: 1 to 8 Gas Block Size: .750 Barrel Thread: 5/8 x 24; Gas System Length: Pistol Length