Surefire closed tine flash hider, this one,
www.surefire.com
77gr TMK (tipped match king) 5.56.

SFCT-556-1/2-28 Closed-Tine Flash Hider | SOCOM Closed-Tine Flash Hider for 5.56 mm (.223 Caliber) Rifles | SureFire
SureFire adapters serve as rock-solid, precision mounting platforms for SureFire SOCOM Fast-Attach Suppressors, as well as, serving as a standalone muzzle device.

77gr TMK (tipped match king) 5.56.