Abstract: A barrel locking mechanism for a break-open-action gun having a barrel and a mechanical section rotatably engaged with each other by a hinge-pin. It has a lug secured to the barrel and having a delining surface. While a stationary receiver is integrally mounted on the mechanical section. On the top of it, a movable receiver having a delining surface corresponding to that of the lug is vertically movably mounted through a spring. When the gun is locked, the lug moves downwards depressing the movable receiver against the spring. As a result, intimate contact of the corresponding surfaces is obtained in order to receive the load when the gun is discharged.