This is a Dead Air Armament Front Cap chambered in 556NATO, model DA201.
This front cap optimizes your Sandman silencer by reducing the front cap size to your caliber. For example" the 5.56 front cap greatly reduces first round pop" and decreases the muzzle reading by roughly 1 to 3 dB.
Features:
Reduces front cap size to proper caliber
Can reduce the muzzle reading by 1 to 3 dB