front of hollow 5 across breech block 3 and over onto breech plate 4 deflecting blade 6 illustratively made from spring steel is divided by slits 7 into several flexible tongues or blades 8 the upper position of the deflecting blade 6 illustrated in broken lines represents the position in which the rear of the chamber 2 is fully closed in the latter position the breech block 3 tightly seals the loading chamber 2 guide plate 9 at the forward end of the device is spaced uniformly a predetermined distance from breech block 3 so that a pocket is created into which deflecting blade 6 can be pushed guide plate 9 is fastened at both ends to breech block 3 as can be seen in fig1 and is tapered to join smoothly with it when deflecting blade 6 is located in its working position locating pins 11 as shown in fig2 which are fixed in radial holes 12 mate with positioning holes 13 in deflecting blade 6 thereby holding it in a predetermined position illustratively positioning holes 13 extend only partially through blade 6 to release blade 6 index pins 11 are depressed by means of a tool applied through holes 14 located above them thereby disengaging pins 11.