High-explosive incendiary/armor-piercing ammunition (HEIAP) is a form of

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...

which combines armor-piercing capability and a

high-explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...

effect. In this respect it is a modern version of an armor-piercing shell. The ammunition may also be called semi-armor-piercing high-explosive incendiary (SAPHEI) Typical of a modern HEIAP shell is the

Raufoss Mk 211 The Raufoss Mk 211 is a .50 BMG (12.7×99mm NATO) multi-purpose anti-materiel high-explosive incendiary/armor-piercing ammunition projectile produced by Nammo under the model name ''NM140 MP''. It is commonly referred to as ''multipurpose'' or '' ...

designed for weapons such as

heavy machine gun A heavy machine gun (HMG) is significantly larger than light, medium or general-purpose machine guns. HMGs are typically too heavy to be man-portable (carried by one person) and require mounting onto a weapons platform to be operably stable or ...

s and

anti-materiel rifle An anti-materiel rifle (AMR) is a rifle designed for use against military equipment, structures, and other hardware (materiel). Anti-materiel rifles are chambered in significantly larger calibers than conventional rifles and are employed to elimi ...

s. The primary purpose of these munitions is armor penetration with better beyond-armor effects. Similarly to SLAP rounds (

saboted light armor penetrator The saboted light armor penetrator (SLAP) family of firearm ammunition is designed to penetrate armor more efficiently than standard armor-piercing ammunition. In the US it was developed by the Marine Corps during the mid/late 1980s and was appr ...

) which get their armor-piercing ability from the propulsion of a 7.62 mm

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

heavy alloy bullet from a 12.7 mm barrel (.50 caliber) using a sabot with much more energy than is usually possible from a 7.62 mm round, HEIAP munitions utilize a similar theory with an added explosive effect at the end. The special effect is developed when the round strikes the target. The initial collision ignites the incendiary material in the tip, triggering the

detonation Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with s ...

of the HE charge. The second (

zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...

powder) incendiary charge will also ignite. This burns at a very high temperature, is not easily extinguished, and can last up to 15 minutes. The remaining element of the round is the

tungsten carbide Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into ...

penetrator. This has a large amount of

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acc ...

and will penetrate the armor as a solid-cored armor-piercing shot would. This takes the incendiary material and about 20 steel fragments (created by the explosives), delivering them in a 25–30 degree cone through the armor, increasing lethality. The triggering of the explosive charge is dependent upon the resistance of the target. If the target offers little resistance then the lack of

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of ...

al heating will prevent the incendiary from igniting and the high explosive from detonating. Larger guns such as the British 30 mm

RARDEN The L21A1 RARDEN ("Royal Armament, Research and Development Establishment" and "Enfield") is a British 30 mm autocannon used as a combat vehicle weapon. The Royal Armament Research and Development Establishment (RARDE) and the Royal Small Arms ...

cannon fire APSE (armor-piercing special effects) shells, which are armor-piercing rounds with added HE effects.

References

See also