Hello, I have a MA legal (pinned/welded) MCX Virtus. Really love this rifle. I am thinking about buying a 300 blackout barrel 16in and a pistol brace (foldable/adjustable). What is the legality of doing so? Would I be in the clear or is it something that I will have to register? Not looking to go SBR... just want to play with another caliber. And as far as I know, pistol braces are not considered stocks? Thanks!!!