The M&P rifles tend to have 14.5 inch barrels, with a 1.5" blind pinned on flash hidder. If you are able to remove it, you have a SBR. Why don't they make a true 16" threaded barrel, so you can add a brake, or a flash hider of your own choice. What's a difference of the barrel being 1.5 inches longer? Why do they do what they do?