Abstract: This invention relates to a knocking-down septum comprising a steel shutter structure on the slats of which a granulated material rests. The granulated material may consist of granules of natural or synthetic rubber, also of recovery rubber and possibly of a self-extinguishing type of rubber, of dry sand, or of a mixture of sand and rubber or the like. This granulated material lies on the slats of the shutter structure in accordance with the shutter's natural angle of repose and is thereby retained by the shutter. When a bullet crosses the thickness of the granulated material the granulated material slows down the velocity of the bullet.