A method of manufacturing a metallic case of a pyrotechnical igniter having a wall with at least one weak zone and an inner surface in the case with at least one part facing this at least one weak zone includes positioning the case on a matrix having a plane zone. The method further includes striking the wall with at least one punch so as to, in a single movement of striking, deform at least the part of the inner surface facing this at least one weak zone and having at least one initially curved-in zone in order to bring it on the plane zone and to form in this manner a plane inner surface, and to form the at least one weak zone.