The fixed Q.F. round is used in the 3.7 cm Pak (anti-tank gun) and has a shell painted aluminium colour with a yellow band midway between the fuze and driving band. There is only one driving band. The overall length of the round is 13.5 inches and the weight 2 lb. 11 oz. The number "6331" or "6331 St." is stamped in the base of the case in addition to "3.7 cm Pak".

Fuze A.Z. 39 or 3,7 cm Kpf.Z.Zerl.P.

H.E. shell filled P.E.T.N./Wax with tracer.

Cartridge case No. 6331 (brass) or 6331 St (Steel).

Propellant charge of tubular double-base type with an igniter or nitrocellulose pow-der and a decoppering agent of pure lead.

Percussion primer C/13 n.A.

Fuze A.Z. 39 is described in Pamphlet No. 4. The fuze "3.7 cm Kpf.Z.Zerl.P." is somewhat similar in appearance but has a red tip and a stamped with the designation of the fuze, the stamping being coloured red. The fuze is fitted with a centrifugal safety bolt which is retained in the safe position, obstructing the movement of the needle, by a powder pel-let. A flash channel connects the powder pellet with a detonator which sets back on to a needle on acceleration and ignites the powder. The combustion of the powder leaves the bolt free to be displaced by centrifugal force. The needle with the hammer is then only held off the detonator by creep.

The interior of the shell is divided into two parts by a diaphragm formed in the shell. The forward compartment is screwthreaded to receive the fuze and the compartment to re-ceive the tracer. The driving band is wholly of copper and is fitted approximately at the centre of the shell with a groove behind it to receive the mouth of the case.

The bursting charge, in the front compartment of the shell, consists of approximately 1 oz. of P.E.T.N./Wax 90/10 in a cup-shaped aluminium container. The container is closed at the mouth by a leather or composition washer over a paper washer.

The tracer consists of a steel cup containing tracing and priming composition and has an external screwthread for assembly in the rear compartment of the shell.

The case is 9.8 inches in length and has a slight increase in taper near the mouth. The steel case identified by the letters "St" following the number "6331" stamped in the base, is coated with brass.

The charge consists of tubular cords about 6.8 inches long with an external diameter of 0.098 inch and an internal diameter of 0.01 inch. The weight of the charge is approxima-tely 5 oz. 11 dr. A small igniter is secured to the base of the charge by a silk strip which extends up the side of the charge. The igniter contains 34.2 grains of nitrocellulose pow-der in granular form.

The propellant is black in colour and consists basically of nitrocellulose and diethylene glycoldinitrate.

"162 g. Digl.R.P. –8.2– (175 x 2,2/0,85)".

The primer C/13, is of the normal German type with a diameter of 0.63 inch at the base and a length of 0.55 inch.