The shell is used in the Q.F. 100 mm 17 calibre howitzer, with a separate loading Q.F. cartridge, and is designed with a "hollow" at the forward end of the bursting charge for the porforation of armour by blast.

The markings and dimensions of the shell, for identification, are shown in the drawing. The weight of the filled projectile is approximately 23 lb. 2 oz.

The streamlined body of the shell has a comparatively thin wall, and is fitted with a cop-per driving band and a pressind-in mild steel base plate. An external screw-thread is for-med at the head for attachment of the dome-shaped impact cap of light alloy, which brings about the function of the base graze fuze and the detonation of the bursting charge at an effective distance from the target. Internally a screw-threaded recess is formed in the base of the cavity for the insertion of the fuze. The walls of the cavity are treated with paraffin wax. The weight of the empty shell, without fuze, is 18 lb. 10 oz.

An exploder, consisting of two pressed pellets of cyclonite/way (one solid and the other perforated) wrapped together in a waxed or varnished paper wrapper, is fitted over the paper sleeve covering the gaine fitted to the fuze. The solid pellet weighs 540 grains and contains a small quantity of pink dye. The perforated pellet weighs 332 grains. The paper wrapper is marked "Det. Sec. A.E.–T4F 5 per cent N 2 MOD 38".

The bursting charge is cast at a density of 1.63 and consists of 3 lb. 9 oz. of cyclonite/ T.N.T. (60/40). The cavity or hollow formed in the head of the bursting charge is ap-proximately parabolic in shape, and is supported by a steel liner, which is secured by the impact cap and has a maximum diameter of 2.85 inches and a thickness of approximately 0.047 inch.

Fig. 19

Italian Q.F. 100/17 mm H.E. Shell with Hollow Charge

The fuze is of the detonating type, with a graze action, and is screwed into a recess in the base of the shell cavity.

The cylindrical body contains a screwed aluminium pellet holder, and is closed at the top by a screwed plug which fits over the fixed striker in the pellet holder and carries the gaine. The body is open at the base.

The pellet holder has a central recess which contains the graze or inertia pellet, and is closed at the base by a screwed cap of aluminium. The recess reduced in diameter near the top to engage the shearing wire fitted in the pellet. An adjacent recess is fitted with a detent and spring in an aluminium sleeve. The detent supports a brass locking pin which locks the centrifugal bolt, between the striker and detonator, in a transverse channel formed in the holder. The channel is closed at each end by an aluminium disc. The centrifugal bolt is a hollow cylinder of aluminium with an aperture to receive the locking pin. Two channels extending through the length of the holder are closed at the top by aluminium discs, and at the base communicate with the recess containing the graze pellet. These, in conjunction with escape holes formed below the detonator in the pellet, are apparently intended to provide an escape for the pressure if the detonator is accidentally initiated. The steel striker, with four flash-holes formed round it, is screwed into a projection on the top of the holder.

The brass gaze pellet is held in position in the holder by the centrifugal bolt and is fitted with a protruding shearing wire which does not come into contact with the holder until the shell is in flight. The detonator in the head of the pellet is of the igniferous type, and consists of a copper sleeve with an inner cup of tinfoil which contains 0.77 grains of a composition consisting of:– Mercury fulminate 11 per cent, potassium chlorate 50.5 per cent, antimony sulphide 38.5 per cent. A recess below the detonator communicates with escape holes leading to the exterior of the pellet.

A description of the 0.89 cyclonite gaine fitted to the fuze is included in this pamphlet.

On acceleration the detent and locking pin set back, thereby releasing the centrifugal bolt. During this period the bolt is held by the set back. During flight the bolt is moved clear of the graze pellet and the striker by centrifugal force, and deceleration causes the graze pellet to creep forward until its shearing wire fouls the step at the forward end of the recess in the holder. The igniferous detonator in the pellet is then very near to the fixed striker and is only held clear by the shearing wire. On graze the shearing wire is overcome and the pellet carries the detonator on to the striker. The flash produced pas-ses through the flash-holes round the striker and initiates the lead azide and styphnate filling which brings about the detonation of the cyclonite filling of the gaine.