I just bought a Masterpiece Arms Mac11 online that I picked up today from my local shooting range. The gun has a rail on the bottom. The guys at the store advised me not to put a foregrip on it. They said that someone could make the argument that would make it AOW. They said it is currently a pistol, but someone could say pistols are one-handed guns, and a foregrip would turn it into something else. Are they being paranoid or was that good advice?