An antidismantling device for preventing dismantling of a hand-gun when a cartridge is present in the barrel (102) of the hand-gun, the barrel (102) being mounted in a breech block (110), and a guide pin (123), which is biased at least indirectly in the direction of the longitudinal axis of the barrel (102), is slidably mounted in a bearing (113) in the breech block (110), and one end of the guide pin at least indirectly abuts a contact surface (121) for making contact with part of a cartridge (101), and the position of the guide pin in relation to the breech block (110) when a cartridge (101) is present in the barrel (102) differs from the position thereof assumed in the absence of a cartridge (101) in the barrel (102) is created in that the guide pin (123) interacts at least indirectly with a safety mechanism (141) provided on the grip of the hand-gun in order to prevent dismantling of the breech block (110) when a cartridge (101) is present in the barrel (102) of the handgun.