I know that being in possession of a short barrel for a rifle is considered constructive possession of a SBR but is being in possession of a stock for a pistol also constructively possessing a SBR? I know that pistols can be converted to rifles by adding a full length barrel and then adding the stock. This leads me to believe that it may be possible to possess an extra unattached stock for a pistol but I wanted to know if anyone knew the official ruling on this.