It's like an MP5 and 516 hybrid... the SIG MPX-C

[skullybones]

That's not a muzzle brake, it's the inside of the suppressor that's on it. That's what the baffles look like, one solid piece instead of the old K syle. So it is more than likely an SBR, oh, and the stamp for the suppressor.

Unless they are one piece.