Cutaway models of several 20x139 shells by D.J. Harms

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1 Cutaway models of several 20x139 shells by D.J. Harms It was originally designed by Hispano-Suiza in the 1950s for their HS 820 cannon, which they saw as the natural successor to the HS 804. Hispano-Suiza was taken over by Oerlikon in 1971, after which the HS 820 was renamed the Oerlikon KAD. The cartridge has been successful, mainly because of its use in the popular Rheinmetall Rh 202 cannon. It is also chambered in the GIAT F2 / 20M693, which is made in South Africa as the Vektor G1-2. These guns have seen various uses, as naval and land-based AA, light AFV armament and in helicopters. The shells are produced by a number of countries: Germany, Switzerland, Netherlands, Italy, South Africa, Norway, France, USA. Functioning of the self destruct delay mechanism disc, as used in projectiles of type 2, 3 & 5: The disc is placed below a spring tensioned ring that exactly fits the hole in the centre of the disc. The ring wants to push the firing pin down by it s disc into the detonator, however the ring is held in upward position by the release (R), which prevents it from moving down. The release has a hook on one end (green arrow) which rotates around a pivot pin (P2). It is held in position by a banana shaped hook which pivots around a pin (P1). It hooks in the release (green arrow). The banana shaped hook is held in position by a leaf spring (blue arrow). On firing, the weight (W) is thrown outward, enabeling the leaf spring to move outward. As long as the centrifugal force is large enough and the weight (W) is thrown outward, the two parts hook into each other (green arrow). As soon as the centrifugal force decreases, the rotation spring surrounding the pivot (P1) starts to push the weight (W) inward, releasing the hooks (green arrow). The release (R) can now move outward, enabeling the ring to pass through the centre hole and push the firing pin down into self destruct. 20x139 DM91 High explosive incendiary - tracer - self destruct (HEI-T-SD) MP (Multi purpose) The projectile has a steel body with a screwed in aluminium nose piece. The upper part of the body and the nose piece are filled with thermite, the lower part of the body is filled with an explosive charge. The projectile has a tracer with a pyrotechnical self destruct mechanism, which ignites the explosive charge if the target is missed. The projectile has no safety features and is ignited by impact energy. The explosive charge is ignited by the thermite charge. The force to ignite the cartridge must be conciderable (impact), dropping it or a loading mishandling cannot ignite the projectile. This projectile has been manufactured by Ra (Raufoss), and as far as I know the projectile is of Norwegian (Raufoss) design.

2 20x139 M599 High explosive incendiary- tracer -Self destruct (HEI-T/SD), fuzed with the AZZ M594A1 (Aufschlag- Zerlege-Zünder / Impact self destruct fuze). The projectile body is made of mild steel, a hole has been drilled in the base to house the tracer element. Weight of projectile: 0,120 kg. Vo.: m/s Length of complete cartridge: 213 mm. The cartridge has been manufactured in The Netherlands by the NWM Functioning of the fuze AZZ M594A1: The fuze has three safety s; -The ball housing the detonator is out of line with the firing pin. -The ball is fixated by a red copper U shaped clamp that only opens on rotation. -A spiral wound metal tape just below the ball that prevents the firing pin from moving forward into the detonator, and only unwinds after firing. On firing, the rotation bend open the copper clamp, enabeling the ball to move freely. The force of the rotation will throw the heavy part of the ball outward, thereby turning the detonator channel in line with the centerline of the projectile. At the same moment the spiral wound metal tape unwinds, releasing the firing pin and enabeling it to reach the detonator. The firing pin is made up of a needle with a disc shaped part just below the top. On this disc, a ring rests which is pushed down by the central spring, surrounding the stem of the hammer pin above the firing pin. The firing pin is prevented from moving down into the detonator by the Mechanical self destruct disc, up to the moment where the ring under the spring is enabled to move down through the disc, pushing the firing pin into the detonator and self destruct occurs. 20x139 DM101A1 High explosive incendiary shell with a base fuze (HEI-T-SD). The projectile is fuzed with the DM771B1 self destruct base fuze. The projectile has a mild steel body, filled with a 4,1grams explosive incendiary charge Hexal (Hexogen/aluminium). A small -1,7 grams- incendiary Zirconium/Hafnium (black) charge on top of the explosive charge that increases the blast working of the explosive charge. A 3,4 grams thermit incendiary charge (red) is placed in an aluminium ballistic cap on top of the projectile. Weight of projectile: 0,120 kg. Vo.: m/s Self destruct at appr m The cartridge has been manufactured in Germany

3 Functioning of the fuze DM77B1: The fuze has three safety s; -The ball housing the detonator is out of line with the firing pin. -The ball is fixated by a red copper U shaped clamp that only opens on rotation. -A spiral wound metal tape just below the ball that prevents the firing pin from moving forward into the detonator, and only unwinds after firing. On firing, the rotation bend open the copper clamp, enabeling the ball to move freely. The force of the rotation will throw the heavy part of the ball outward, thereby turning the detonator channel in line with the centerline of the projectile. At the same moment the spiral wound metal tape unwinds, releasing the firing pin and enabeling it to reach the detonator. The firing pin is made up of a needle with a cylindrical hammer piece. When armed the firing pin is kept away from the detonator by a weak spring. Below the hammer piece, the mechanical self destruct mechanism disc is placed, facing downward. Below this disc, a spring is placed that pushes the firing pin with the hammer piece upward on self destruct. 20x139 HEI, type designation unknown, of Swiss design. The original design of the 20x139 goes back to the 50 s of the last century. The Hispano Suiza factory designed and produced the 20x139 for the HS-820 gun as a replacement for the 20x110 HS804, the Oerlikon factory designed and produced a comparable cartridge, the 20x129. When the Hispano factory was bought up by the Oerlikon company in 1971, the Hispano s 20x139 cartridge was pushed out in favour of the 20x129, allthough this type of cartridge was much less popular than the 20x139. Most country s using the 20x139 than took up the production of cartridges themselves. It can be clearly observed that the mechanical self destruct fuze s internal parts and functioning are exactly the same as the Hispano s 20x110 AAA cartridge. Functioning of the fuze: Inside the fuze body, an aluminium self destruct piston is placed, housing four steel balls and the a spring that wants to push the piston down. The piston rests on two brass chamfered centrifugal safety pins, placed in a radial position compared to the fuze body and whom prevent the piston from moving down and the firing pin from reaching the detonator. The lower part of the firing pin has a disc shaped part which is positioned under the piston; on impact the firing pin can move down, on self destruct the firing pin is pushed down by the piston, pushing the disc of the firing pin down. A thin walled brass cylinder chamfered on the inside upper edge- is placed around the piston. Upon firing, the set back force pushes all parts downward, preventing the fuze from arming. At a safe distance from the gun the centrifugal force throws all parts outward. The chamfered edges of the two brass pins climb the chamfered edge on the inside of the brass detonator housing, pushing the brass cylinder upward and releasing the aluminium piston. This piston however is locked in position by the four balls thrown outward into the chamfered edge inside the brass cylinder. The firing pin is now free floating, on impact it is hammered into the detonator. If no target is hit, a moment will occur where the force of the spring inside the piston is larger than the locking force of the four balls in the chamfered edge of the brass cylinder. The balls will now be pushed back into the piston, allowing the piston to move down, pushing the firing pin into the detonator by means of the disc on the firing pin.

4 20x139 DM51A1High explosive - tracer (HE-T), fuzed with the impact self destruct fuze DM131A1. The projectile has a mild steel body DM 1027and a hole drilled in the base that houses a tracer. The Incendiaryexplosive charge of mixture 891 has been pressed in the body. Weight of projectile: 0,122 kg. Vo.: m/s The cartridge has been manufactured in Germany. Functioning of the fuze: After firing, the sprial wound metal tape unwinds, enabeling the firing pin to reach the detonator on impact. A mechanical self destruct mechanism disc is placed above this spring, destroying the projectile if no target is hit after appr sec. of flight. 20x139 DM43 Armour piercing - tracer (AP-T). An aluminium projectile body, housing a tungsten carbide core. The nose of the projectile is filled with a MX-71 magnesium incendiary / flash charge which shows the point of impact on the target. Weight complete cartridge: 0,31 kg. Weight of projectile: 0,111 kg. Vo.: m/s 1000 m: 32 mm at 90, 24 mm at 60, 8 mm at 30 The cartridge has been manufactured in Germany.

5 20x139 DM63 Armour piercing discarding sabot tracer (APDS-T) The projectile is made up of three main components; -the aluminium base, housing the driving belt and the core -the tungsten carbide core with an aluminium ballistic cap -the nylon sabot. After leaving the barrel, the sabot rips open over four weakening lines and is blown away. An endless spring fixates the tungsten core in the aluminium base, only after firing will the centrifugal force widen the diameter of the spring enabeling the core to seperate from the aluminium base piece. Weight complete cartridge: 0,31 kg. Weight of projectile: 0,108 kg. Vo.: m/s Penetration: 35 mm armour steel plate at The cartridge has been manufactured in Holland (NWM).