Disclosed is a metallic cover cap for sealing a metallic bottle, comprising a gasket provided with a flat central zone and an annular zone which includes an outer rim and an inner rim that are separated by a notch, such that the outer rim extends axially, continues circumferentially, and includes: a first surface; a second surface with a flat portion and a concave portion radially opposite the notch; and a third flat surface that extends between the first and second surfaces, and the inner rim extends axially, continues circumferentially and spaced radially inwards of the first rim, and includes: a first flat surface opposite and perpendicular to the flat zone; a second concave surface radially opposite the notch; and a third flat surface between the first and second surfaces that is inclined toward the notch.