The CAGE (Concussion Altering Gas Expansion) Device is the pinnacle of concussion reduction technology, designed to disrupt side concussion while keeping or enhancing the characteristics of your Aero's Gamma and Epsilon muzzle devices. It features a close wrap fit and a pattern of small holes for more uniform energy expenditure at a slower pace leading to smoother recoil and zero muzzle flip by "bleeding off energy" rather than abruptly losing energy. NOTE: The CAGE device does not include the muzzle brake. It is compatible with dual-chambered muzzle devices, Gamma/Epsilon 556, Gamma 556 EX, and Gamma 300BLK.This model is constructed of stainless steel with a black nitride finish.