A mechanical initiating system (10) for caseless ammunition including a weapon breech block and a powder body chamber adjoining the weapon breech block. A firing pin is axially displaceably arranged in a through hole (26) formed in the weapon breech block. A powder body, which can be initiated by the firing pin and having a priming device, is arranged in the powder body chamber. In order to achieve a reliable and simple sealing between the firing pin and the inside wall of the through hole, the weapon breech block has a grease reservoir which is open facing towards the through hole, and the firing pin is peripherally provided with at least one grease groove.