Abstract: A breechblock system for a gun includes a breechblock; a firing pin slidably received in the breechblock and having two diametrically oppositely located catch recesses; and two locking levers pivotally supported by the breechblock on opposite sides thereof and each having first and second arms. The two locking levers have a locking position and an unlocking position. In the locking position the first arm of the respective locking levers projects into the respective catch recesses for preventing the firing pin from moving from its locked position into its firing position. Further, two bolts are provided which are movably supported on opposite sides of the breechblock and which cooperate with the breechblock and with respective locking levers. The bolts have a withdrawn position and an advanced position. In the withdrawn position the bolts are out of a depressing engagement with the respective locking levers, whereby the locking levers are maintained in the locking position by a force-exerting arrangement.