High Explosive Incendiary/Armor Piercing Ammunition
From Wikipedia, the free encyclopedia
High Explosive Incendiary/Armor Piercing Ammunition (HEIAP) is a form of shell which combines both an armour piercing capability and a high explosive effect. In this respect it is modern version of armour piercing shell.
Typical of a modern HEIAP shell is the Raufoss Mk 211 0.50 inch round designed for anti-materiel weapons such as heavy machine guns and anti-materiel rifles
The primary purpose of these munitions is armor penetration, but unlike SLAP rounds (Saboted-Light Armor Penetrator) which get their armor piercing ability from the propulsion of a 7.62mm tungsten heavy alloy bullet from a 12.7mm barrel (.50" cal.) with much more energy than is usually possible from a 7.62mm round (plus the fact that a tungsten alloy bullet will completely destroy the rifling of the barrel—hence the plastic sabot), the HEIAP munitions use high explosives to "blast a path" for the penetrator.
The round is loaded just as solid full metal jacketed round would be. The special effect is developed when the round strikes the target. The initial collision ignites the incendiary material in the tip, triggering the detonation of the HE charge. The second (zirconium powder) incendiary charge will also ignite. This burns at a very high temperature and is not readily extinguished and can last for 30 seconds.
The remaining element of the round is the tungsten carbide penetrator. This has a large kinetic energy and will penetrate the armour as solid-cored armour piercing shot would. This would take some of the incendiary round through the armour. The MK 211 is claimed to penetrate up to 2 inches (50 mm) of rolled steel.
The trigger is dependent in on the resistance of the target. If the target offers little resistance then the lack of frictional heating would prevent the incendiary from igniting and therefore the high explosive from detonating.
Larger guns such as the British RARDEN cannon of 30 mm fire APSE (armour piercing secondary effects) shells which are an armour piercing round with added HE effect.
