The shell body is hardened throughout, the hardness diminishing from nose to base. The penetrative cap is attached to the shell by a low temperatur soldering process. Both the shell (which is machined from rolled bar) and the penetrative cap are of 1 per cent chro-nium steel. The ballistic cap is attached to the penetrative cap by spot welding and va-ries in thickness from 0.037 inch at the nose to 0.057 inch at the base. The driving band is secured in the groove by longitudinal knurling and consists of soft iron under a copper exterior. An aluminium container for the bursting charge is set in the shell by means of a coal tar bitumen and a pad of the same material fits the reduced forward end of the ca-vity.

The bursting charge, weighing 83.3 grams (2 oz. 15 dr.), consists of a 33.9 gram cast pellet of T.N.T. at the forward end, a 21.5 gram cast pellet of T.N.T. with a central per-foration containing a 10.4 gram pressed pellet of P.E.T.N./Wax in the intermidate position and a 17.5 gram cast pellet of T.N.T. adjacent to the fuze. This base pellet and the P.E.T.N./Wax pellet are designed to accommodate the forward end of the fuze. The space between the filling and the fuze body is taken up by an aluminium washer with pa-per and cardboard washers between it and the filling and a cardboard washer behind it. The weight of the shell is approximately 14 lb. 13 oz.

Fig. 15

The base fuze, which includes a gaine fitment, is shown in Fig. 16. The steel inertia pel-let, containing the igniferous detonator, is held away from the needle in the safe position by five centrifugal segments. The segments are held in the safe position by the expand-ing spring ring. The steel adapter carrying the needle has four flash holes in its base, which lead to the cavity formed in its interior. The cavity is closed at the front end by a brass plug which has a small central flash hole coinciding with a hole in the base of the gaine plug. The gaine consists of an aluminium plug containing a mixture of lead azide and lead styphnate at its perforated base end and P.E.T.N./Wax at ist forward end. The forward end is closed by means of an aluminium cap and the gaine is attached to the steel adapter in the fuze body by means of the aluminium dome.

Mercury fulminate

8.1 per cent.

Potassium chlorate

59.7 per cent.

Antimony sulphide

29.4 per cent.

Glass

2.8 per cent.

Details of the tracer which screws into the base of the fuze are not available.

Centrifugal force set up by the rotation of the projectile in flight causes the segments to rotate on their axis against the expanding spring ring and, one after another, their inner ends move clear of the inertia pellet. There is no creep spring. On impact the inertia pel-let sets forward and impinges the detonator on the needle. The resultant flash passes through the small hole in the brass plug into the gaine. The combination of the adapter cavity and the small hole in the brass plug is apparently intended to act as a short delay by expansion of the flash within the cavity.

Details of the cartridge and primer are given in the section describing the H.E. round.

Fig. 16 – Fuze, 7.5 cm A.P. Shell.