In an externally powered firing weapon the danger exists with an ignition delay or hangfire condition that the cartridge still is ignited after the positively reciprocated breechblock has been unlocked from the weapon barrel. The safety apparatus in accordance with the invention prevents, in case of an ignition delay, firing of the cartridge after unlocking of the positively reciprocated breechblock. Heretofore known safety devices of this type are complicated and a substantially simple design is strived for. The safety apparatus in accordance with the invention automatically decouples the breechblock carrier from the breechblock head when the breechblock head is locked in the weapon barrel. The device responding to an ignition delay prevents unlocking of the breechblock head from the weapon barrel and coupling of the breechblock carrier with the breechblock head. The breechblock head locked by means of a rotary lock to the weapon barrel and the breechblock carrier are preferably coupled together by means of a rotary coupling.