An adjustable firearm stock has a body defining an elongated channel adapted to receive a rail, the channel having an internal width adapted to receive the width of the head portion of the rail, and opposed elongated hook surfaces defining a hook width adapted to receive the neck of the rail, the hook surfaces bear on the rail to resist separation of the body from the rail, the channel having an elongated floor surface parallel to and opposing the planar mounting surface of the rail, a foot element connected to the body and having a contact surface facing the planar mounting surface of the rail, and a securement facility operably connected to the foot element and to the body, and operable to move the foot with respect to the body to compress the rail between the contact surface of the foot and the hook surfaces.