(Fig. 28)

From imformation received in later reports, the position of the aluminium supporting ring under the driving band of this shell as shown in Fig. 20 of Pamphlet No. 2 is incorrect. This figure and the information given on page 2 under the heading "20 mm Shell" should be deleted.

Fig. 28

The shell body is of drawn steel with thin parallel walls and a hemispherical base. Near the base cannelure is formed for the attachment of the cartridge case and above this a copper driving band is fitted in a groove in the body. An aluminium ring is fitted inside the body coincident with and provinding support for the driving band. A steel ring with an internal screw-thread for the attachment of the fuze is secured in the head of the shell by four indentations.

The bursting charge consists of approximately 262 grains of penthrite/wax. The filling is designed to form a cavity to receive the magazine portions of the fuze and is covered by a paper washer.

The body of the shell is painted yellow with a black ring near the head.

The fuze, which is inserted with a steel washer between its underside and the head of the shell, is the A.Z. 1502. This is a direct action type with its magazine in the form of a brass container fitted to the underside. The container carries a detonator positioned over an intermediary charge of penthrite powder. The needle of the fuze is of the float-ing type and is held off the detonator by two segments assembled under the enlarged head to the needle. The upper end of the segments and the underside of the enlarged head are shaped to retain the segments in position. The segments are further secured by a length of brass tape coiled around them. Positioned in a recess in the nose of the fuze, above the needle, is the hammer, which consists of a short spindle with an enlarged head. The recess is closed by a metal plate.

On acceleration the needle sets back and holds the segments securely. During flight "creep" action and the protection from air pressure provided by the metal closing disc re-sult in a forward movement of the hammer and needle. When the rate of spin has incre-sed sufficiently the coiling of the brass tape is loosened and the segments thrown clear by centrifugal force. On impact the needle is driven on to the detonator by the hammer and the detonation of the bursting charge is brought about through the penthrite powder charge.