Abstract: The present invention relates to a locking element to be insertable into a cartridge chamber of a firearm, the locking element having a proximal end and a distal end. The locking element includes an outer sleeve with a movable operating element provided therein, wherein the sleeve includes a (first) diameter such that the sleeve is snugly insertable into the cartridge chamber from the cartridge chamber side, but the diameter being larger than the diameter of the barrel of the firearm. The at least one blocking element is pressed against the wall of the cartridge chamber if external pressure is applied from the distal end to the operating element.

Abstract: The present invention relates to a locking element (42) to be insertable into a cartridge chamber (420) of a firearm, said locking element having a proximal end (220) and a distal end (260). The locking element comprises an outer sleeve (14) with a movable operating element (16) provided therein, wherein the sleeve (14) comprises a (first) diameter such that the sleeve (14) is snugly insertable into the cartridge chamber (420) from the cartridge chamber side, but said diameter being larger than the diameter of the barrel (6) of the firearm.