(Fig. 10)

The fuze is used in the 4.7 cm A.P.C. shell of Czech origin described in Pamphlet No. 10, pages 29, and differs from that described for the 3.7 cm A.P.C. shell in Pamphlet No. 2, pages 6 and 7, mainly in the addition of a delay sealing plug.

The steel needle pellet and creep spring are contained with the detonator in a cylindrical holder which is screwed into the base of the steel head of the fuze. The head contains the delay arrangement and, at its forward end, carries the gaine.

The delay arrangement consists of a sealing plug which closes the flash hole leading to the gaine and a filling of gunpowder which surrounds the plug. The cylindrical plug has a pintle and copper washer at the top to seal the flash hole and a flange near the base. The clearance between the flange and the wall of the recess in which the plug is contai-ned is 0.015 inch. Below the flange there are four radial channels leading to recess in the base of the plug.

During flight the needle pellet with the two locking balls, moves forward as the result of deceleration, until the ball are in a position to be thrown out-wards by centrifugal force. The needle is then held off the detonator only by the creep spring.

On impact, the needle pierces the detonator and, at the same time, the sealing plug sets forward and seals the flash hole leading to the gaine. The flash from the detonator en-ters the recess in the base of the plug, and passing through the radial channels, ignites the gunpowder. The pressure set up by the ignition of the gunpowder behind the flange presses the plug firmly into the flash hole above. The combustion of the gunpowder leaves the pellet unsupported and leads to the ignition of the gunpowder in front of the flange, through the small clearance between the flange and the wall of the recess. The resultant pressure acting on the front of the flange pushes the sealing plug back into the recess in the forward end of the mechanism holder and thus opens the flash hole leading to the gaine.

Fig. 10