Originally Posted by ChrisO
Probably a Muzzle brake. There are plenty of Muzzle Brakes out there that are designed to look like FH.
except that looks like the Noveske N4 basic 14.5" with pinned Smith Vortex FH.
I think Johnny switched it before he took the Magpul class, cuz i remember seeing a YHM muzzle break in his other thread in the training forum.