controller 632 motor 634 and iris valve 614 interrelated as shown live round 112 is depicted in bore 108 fig7 depicts iris valve 614 in a closed state and fig8 depicts the iris valve in an open state the iris valve comprises a plurality of leaves 736 iris valves typically include a circumferentially disposed rotatable ring that when rotated moves the leaves such that aperture 838 begins to form at the center of the valve the aperture continues to open radially until it reaches its full size in the closed state the iris valve seals barrel 102 against water intrusion for the embodiment of gun 100 that is depicted in fig6 some amount of water will of course be resident in the barrel between valve 614 and muzzle end 106 of barrel 102 when iris valve 214 is closed iris valve 614 is operatively coupled via appropriate linkages not depicted to motor 634 the motor typically an electrical motor drives the opening and closing of iris valve 614 in the previous embodiments valve actuation was u201c automatic u201d in the sense that it was driven by combustion gases but for the embodiment depicted in fig6 the actuation of valve 614 is responsive to information coming from fire control system 110 more particularly fire control system 110 sends a signal to controller 632 at an appropriate time as a function of valve response etc to actuate motor 634 to change the state of valve 614 with regard to timing it is possible that due to the response of valve 614 the valve might need to begin opening before a round is fired in.