Category: Term of the day
A type of chemical energy ammunition (i.e., ammunition where the penetrative power is generated by explosive energy rather than by kinetic energy) fitted with a high explosive anti-tank (HEAT) – or hollow charge – warhead. The HEAT warhead is not velocity dependent. In order to achieve penetration, the limited amount of explosive is shaped into an inverted, rearward-facing cone lined with a metal such as copper or some other ductile material. When the charge is detonated by a nose fuze, a jet of high energy gas and vaporised metal is projected forward at speeds, typically, of 6,000 m per second. This plasma jet acts like a cutting torch.
The detonation of the limited amount of high explosive contained within a shell fired from a tank gun is unlikely to do lethal damage to a tank and therefore a means must be found to focus the energy of the detonation into some form of high-energy jet. The most effective and widely used method is to shape the detonation wave so that the total energy available is directed onto a small cross-sectional area of the target. This is achieved by manufacturing the explosive charge into the shape of an inverted, rearward-facing cone and lining it with copper or some other low melting point, ductile metal. When the charge is detonated by the fuze mounted in the nose, a jet of high-energy gas and vaporised metal from the cone is projected axially forward (the Munroe effect). This jet, travelling at a speed of around 6,000 m per second, burns its way through the armour like a cutting torch. The effectiveness and penetration of the jet depends on the diameter of the cone and hence the calibre of the gun, the type of metal liner and the 'stand-off' distance from the target at which the charge is detonated.
The penetration of a HEAT round is severely degraded if the charge is spun, so the projectile must be fin-stabilised (even at 400 rpm penetration is reduced by about 25%). If the hollow charge is to be fired from a rifled barrel, then some means such as slipping driving bands must be used to limit, or preferably eliminate, the spin. Although a relatively small cone diameter can produce a very impressive depth of penetration (typically 5-6 times cone diameter), lethahty is low unless it over-matches the target by at least 33%. However, if an exit hole in excess of 24 mm in diameter is produced, the terminal effect inside the vehicle is likely to be considerable as the jet continues into the target with considerable residual energy bringing with it 'spall' or splinters torn off the armour plate. Thus, the performance and effect of the hollow charge round is largely dependent on cone diameter.
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