I have owned an AR15 SBR in 7.62mm for some time now and love it. Have had no problems with it. Would like to make some mods to it but am not up on the legality of adding stuff. The lower is registered as a short-barrel. So can a gas piston setup or a three-shot burst trigger setup be installed and still be legit? I do not want to spend the next several years as Bubba's horizontal dance partner.