Explosive i incendiary shells

The term 'shell' is again of ancient origin and obvious meaning: a hard outer casing protecting something more vulnerable inside, in this case a high-explosive or incendiary compound. In larger artillery calibres, shells can contain a wide variety of materials including smoke to obscure visibility, starshell for illumination, chemicals, various anti-personnel rounds, and anti-tank sub-munitions (some capable of homing onto their targets) but these need not concern us here.

Cannon shells were originally made by drilling out a cavity of the appropriate shape in a steel shot to take the desired explosive or incendiary compound. This led to a relatively small capacity in smaller calibres, however, so during the Second World War, German technicians perfected the mine shell (Minengeschoss or M-Geschoss) which was made by stamping and drawing the shell from a thick disc of metal in the same way in which cartridge cases are made. This resulted in a shell with thin but strong walls, with a far larger capacity. It also led to a lighter shell overall (steel being much heavier than explosives), permitting a higher muzzle velocity at the expense of range (as light shells slow down more quickly), which made this innovation particularly suitable for aircraft cannon.

Important but conflicting characteristics of HE fillings are that they must explode as violently as possible to make the most of the restricted quantity of compound that the shell can carry, yet be completely safe over a wide range of temperatures, despite the rough handling the ammunition may receive from the gun mechanism.

Incendiary and even HE projectiles have been used in rifle-calibre ammunition, most notably for .303" (7.7mm) aircraft guns in the Second World War when the RAF made much use of incendiaries, officially known as the De Wilde after a Belgian inventor but modified by Major Dixon of the War

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