1. A BREECH CLOSURE MECHANISM FOR A RECOILLESS GUN COMPRISING: A BREECH BAR HAVING A LONGITUDINALLY EXTENDING SPINDLE AND ROTATABLY MOUNTED ABOUT A FIXED TRANSVERSE POST, AND SPINDLE HAVING TRANSVERSELY APERTURED WALL MEANS, A SPRING BIASED HAMMER LONGITUDINALLY SLIDABLE IN SAID SPINDLE FOR ACTUATING A LONGITUDINALLY MOVABLE FIRING PIN AND HAVING ARCUATE SLOT MEANS AND A PERIPHERAL NOTCH THEREIN, A CLOSURE ROTATABLY MOUNTED UPON SAID SPINDLE AND HAVING A FORWARD APERTURE SLIDABLY RECEIVING SAID FIRING PIN AND ALIGNED WITH SAID HAMMER, A CAMMING MEMBER SECURED TO SAID CLOSURE AND EXTENDING THROUGH SAID APERTURED WALL MEANS AND INTO SAID ARCUATE SLOT MEANS FOR RETRACTING SAID HAMMER UPON ROTATION OF SAID CLOSURE, A SEAR MEMBER SLIDABLY MOUNTED IN SAID BAR AND HAVING ONE END PORTION ENGAGEABLE IN SAID HAMMER NOTCH WHEN SAID HAMMER IS RETRACTED, AND MEANS FOR MOVING SAID SEAR ONE END IN AND OUT OF ENGAGEMENT WITH SAID HAMMER NOTCH.