MasterPiece Arms is now making a short barrel rifle (SBR) version of their 5.7×28 gun. The new SBR has a threaded 8″ barrel for the included muzzle brake, or for the MPA Suppressor (which is shown in these photos but does not come with the gun). Yes, all NFA rules do apply.
The MPA57SST-SBR (aka MasterPiece Arms 5.7×28 SBR) comes outfitted with an MPA short aluminum quadrail and a Strike Industries foregrip. Based on the photos, the foregrip appears to be the “Cobra Tactical” that normally retails for $25.