(Fig. 20)

This fixed Q.F. H.E. round, fired from the 3.7 cm anti-tank gun, is similar to the round described in Pamphlet No. 6 except that the H.E. bursting charge is of T.N.T. This is in-dicated by the H.E. numeral "27" stencilled above the shoulder of the shell. The shell described in Pamphelt No. 6 is normally marked "32" to indicate the P.E.T.N./Wax 90/10 filling.

The shell, fitted with the A.Z. 39 fuze, is painted aluminium colour and has a yellow band about midway between the single driving band and the fuze. This band distinguishes the H.E./T. shell from the normal H.E. shell. The brass case (or steel with a brass coating) is 9.8 inches in length and has the model number "6331", and the designation of the equip-ment stamped in the base. The marking "Sprgr." is stencilled in white also on the base of the case. The length of the complete round is 13.4 inches and the weight, 2 lb. 13 oz. 8 drs.

Fuze A.Z. 39 (described in Pamphlet No. 4).

H.E./Tracer shell.

Tracer No. 3.

Case Model 6331 or 6331 St.

Propellant charge of double base composition with igniter.

Primer Percussion C/13 n.A.

The shell with its upper and lower cavities separated by a diaphragm is the same as that descriped in Pamphlet No. 6. The aluminium container in the upper cavity contains a 14 dram pressed pellet of flake T.N.T. of density 1.56. The lower cavity contains a compa-ratively large tracer. The weight of the empty shell is 14 oz. 8 drs. The weight of the fil-led shell with fuze and tracer is 1 lb. 5 oz. 5 dr.

The case is 9.84 inches long with an increase in taper at 9.25 inches from the base. The external diameters in front of the flange, at the shoulder and the month are 1.81, 1.57 and 1.52 inches respectively. The effective capacity is approximately 17.69 cubic inches (290 c.c.).

The designation of the equipment and the particulars of the propellant charge are sten-cilled in black on the side of the case. The marking "P.T. + 25° C", indicating the charge weight to be based on a standard charge temperature of 25° Centigrade, is also stencil-led on the side of the case in red.

The weight, nature and size of the propellant charge, as marked on the case, is 164 grams of Digl.R.P. – 8.2 – (175 x 2.2/0.85). This marking is repeated on silk tape attach-ed to the igniter bag. The propellant is in tubular form, the dimensions of the smooth black tubular sticks in inches being:– length 6.89, external diameter 0.087, internal dia-meter 0.033. The composition of the propellant, as found by analysis, consists of:– nitro-cellulose 65.12 per cent (Ntirogen content 12.14 per cent), diethylene glycoldinitrate 31.52 per cent, centralite 2.65 per cent, potassium sulphate 0.42 per cent and 0.29 per cent of graphite.

The igniter consists of a circular silk bag to the base of the charge by a silk tape and containing 34.4 grains of the usual geyish green porous nitrocellulose powder in the form of short cylindrical grains. The mean dimensions of the grains are 0.43 inch length and diameter. The composition, a found by analysis, consists of:– nitrocellulose (including graphite) 87 per cent, diethylene glycodinitrate 11 per cent, centralite 0.5 per cent, di-phenylamine 0.5 per cent, and 1 per cent of volatile matter.

The primer percussion C/13 n.A. is described in Pamphlet No. 7. In this instance, as in other of these primers recently examined, the amounth of mercury fulminate in the cap composition has, been decreased and granular gun-powder has been introduced between the cap and the pellet of pressed gun-powder. The cap composition consists of the fol-lowing:– mercury fulminate 30.6 per cent, potassium chlorate 35.2 per cent, antimony sulphide 27 per cent and 7.2 per cent of ground glass.

Fig. 20