A green sheet stack having a cavity is produced, and a shrinkage-reducing sheet containing inorganic powder material, which is not fired in a step of firing the green sheet stack, is prepared. In another aspect of the present invention, body armor inside a jacket is repositionable due to adjustment of a coupled adjustment strap. The aperture of the washer is greater than that of the shaft. By displacement of the opening instant of the charging valves, air can be pumped from the cylindrical combustion chambers into the compressed air tank.