EMPLOYMENT: Used in 4.7-cm H.E. Shell (4.7-cm Pak.Sprgr.) (See fig. 572.)

DATA:

Over-all length: 1.312 inches.

Maximum diameter: 1.0 inch.

Threaded length: 0.312 inch.

Number of threads: 3 RH.

CONSTRUCTION: This fuze is of the direct action detonating type in which the striker is held off the detonator by four steel balls.

The hollow stemmed aluminum striker with enlarged head passes through a cup-shaped ferrule and is supported at the cone, near the point, by four stell balls. The balls are lo-cated in the internally coned metal cup and retained by the ferrule which is pressed on to them by the spiral spring. The cone of the striker corresponds with the coned interior of the cup so that a force acting along the axis of the striker will not displace the balls. The head of the striker is housed in a recess in the cap of the fuze, the recess being closed against air pressure by a copper disk.

The magazine screwed into the undersite of the fuze and contains the initiator composi-tions in a copper capsule over a 48-gram filling of PETN. The copper capsule has a cop-per disk soldered in the front end and a second copper disc, with feld washer attached, interposed between it and the striker point. The initiator filling in the capsule consists of a 25-gram layer of detonating composition over 31 grams lead azide. The detonating composition consists of:

Mercury fulminate 28.7 percent, potassium chlorate 39.8 percent, and antomony sulphide 31.5 percent.

The fuze is fitted with a brass cover secured by a tear-off strip. The strip is provided with a finger ring which is lightly soldered to the cover.

ACTION: The cober is removed before loading. During the acceleration, the balls are held by set-back and the ferrule. When acceleration ceases and the rate of spin is sufficient, the balls are forced outwards by centrifugal force and retained in this position by the ferrule under the pressure of the spring. The striker is then held off from the detonator by creep action. On impact, the striker is driven in and pierces the detonator.

REMAKRS: The copper disc over the initiator capsule is probably intended to act as a re-sistance to the striker and to prevent premature action by wind pressure acting on the striker, such as might occur if the copper disc in the cap of the fuze were punctured.

Neither the striker, ferrule, nor the spring are positively located, and it appears that the striker is so designed that the point of the striker may rove considerably off its normal axis without jamming, which, should it occur, would render the fuze insensitive on a light target.

Figure 572 – Fuze for 4.7-cm Pak. Spgr.