EMPLOYMENT: This fuze was found in a 100-mm projectile. Fragments of this type of fuze were also found with splinters which appear to be from 75-mm and 83.5-mm projec-tiles. (See fig. 589.)

DESCRIPTION: The principal parts of the fuze are the steel body, percussion mecha-nism, setting device for delay or instantaneous action and gaine.

Steel Body. The conical steel body is fitted with a brass nose which can be screwed in or out of the body and forms the means of setting the fuze for instantaneous or delay ac-tion. The lower part of the body is threaded to take the gaine and the upper part hollow-ed, screw-threaded, and sealed with solder. Externally the body given a protective coat-ing (nature not specified) and fitted with a brass cover, soldered on, which is removed before firing.

Percussion Mechanism. The striker (percussion mechanism) is of nickel steel with a head of duralumin screwed on to it. It is protected by a bronze cover plate set into the nose of the fuze and retained with sealing composition. The striker is prevented from striking the detonator before impact by:

1. Four polished nickel steel balls which fit between the striker and the detonator holder.

2. A creep spring which keeps the striker away from the detonator during flight.

3. Four castelated notches formed by cutting and bending the top end of a small tube of sheet iron through which the striker passes.

The detonator (copper tube) is secured in the detonator holder by a screwed plug. It consists of equal parts by weight of fulminate of mercury and inflammable composition. A transverse hole is drilled through the detonator holder to form a seating for the spiral spring which holds the lower set of balls in the circular run in the body.

The detonator holder is seated in a brass tube which has at its lower end two semicircu-lar notches which retains the lower set of balls in position before firing. The upper part of the tube has three equidistant rectangular notches through which the upper set of balls pass by centrifugal force after firing and two lateral grooves in which the lower set of balls are forced when the brass tube sets back on firing.

The delay holder contains two parallel delay fillings of loose powder and compressed powder. The holder has a central fire channel which, when the nose of the fuze is un-screwed, is closed by a ball.

Setting Device – Instantaneous Action. The nose is screwed into the body and its lower portion, being coned, displaces the ball from the central channel. The flash from the de-tonator can then pass direct through the continous central channel of the fuze.

Delay. The nose is unscrewed and the ball, due to gravity, closes the central channel. The flash from the detonator can then only pass through the transverse channels in the base of the nose and so through the delay filling to the gaine.

After unscrewing, and with the ball closing the central channel, the nose of the fuze must then be screwed in again in order to seal hermetically the junction of the ball and channel and to prevent the ball from moving out-wards due to centrifugal action in flight.

The amount of unscrewing is limited by a ball which is carried in a seating in the body and is free to move in a groove out in the threaded portion of the nose.

The gaine, of steel varnished black, is screwed into the lower part of the fuze. It con-sists of a detonator, exploder, and safety devices.

The detonator consists of fulminate of mercury and compressed TNT grains carried in a holder and retained by a washer.

The exploder consist of TNT pellets in varying degress of composition and are held in a brass tube. The bottom of the gaine is filled with a larger charge of TNT.

The safety device consists of a rotating bolt containing an explosive pellet. The normal position of the bolt is at right angles to the axis of the fuze where it is retained by a ring held in position by a spiral spring. A ball limits the upward movement of the ring. In this position the explosive pellet in the bolt is at right angles to the axis of the fuze, there is, therefore, no communication between the detonator and the exploders.

On firing, the ring sets back compressing its spring.The ball, which is designed to prevent the upward movement of the ring, is now free to move out-wards under centrifugal for-ce.

On acceleration after the shell has left the bore, the ring is forced forward by its spring and this movement rotates the bolt through 90°. The pellet in the bolt is then in line with the axis of the fuze and completes the transmission of the detonation to the exploders.

ACTION: On firing, the brass tube which retains the lower set of balls in position, sets back. The balls are thrust into the hole of the detonator holder, pass along the grooves and return in the circular runway. Centrifugal force causes the upper set of balls to pass one after the other through the upper notches of the brass tube and come to rest in the runway of the fuze body. Allowing the balls to escape one at a time is an added safety device against prematures.

During flight, the striker is kept from the detonator by the creep spring and by the not-ches cut in the sheet iron tube in the nose. The detonator holder is held by the lower set of balls, bearing in the circular runway.

On impact, the striker is forced inwards, stripping the notches of the tube and compres-sing the creep spring. The detonator holder slides through the brass tube overcoming the resistance of the lower set of balls and is carried on to the striker.

Figure 589 – Skoda Percussion Fuze