Armor - piercing shot and shell An armor - piercing ( AP ) shell is a type of ammunition designed to penetrate armor . From the 1860s to 1950s , a major application of armor - piercing projectiles was to defeat the thick armor carried on many warship s . From the 1920s onwards , armor - piercing weapons were required for anti - tank missions . Furthermore it is used to defeat concrete , ballistic vest s , bulletproof glass , and other defenses . An armor - piercing shell must withstand the shock of punching through armor plating . Shells designed for this purpose have a greatly strengthened case with a specially hardened and shaped nose , and a much smaller bursting charge . Some smaller - caliber AP shells have an inert filling , or incendiary charge in place of the HE bursting charge . The AP shell is now little used in naval warfare , as modern warships have little or no armor protection , but it remains the preferred round in anti - tank warfare , as it has a greater " first - hit kill " probability than a high explosive anti - tank ( HEAT ) round , especially against a target with composite armor , and because of higher muzzle velocity , is also more accurate than a HEAT round . Armor - piercing cartridges are also available as small arms ammunition , primarily for use as an anti - matériel round or to defeat body armor . History . The late 1850s saw the development of the ironclad warship , which carried wrought iron armor of considerable thickness . This armor was practically immune to both the round cast - iron cannonballs then in use and to the recently developed explosive shell . The first solution to this problem was effected by Major Sir W . Palliser , who invented a method of hardening the head of the pointed cast - iron shot . By casting the projectile point downwards and forming the head in an iron mold , the hot metal was suddenly chilled and became intensely " hard " ( resistant to deformation through a Martensite phase transformation ) , while the remainder of the mold , being formed of sand , allowed the metal to cool slowly and the body of the shot to be made " tough " ( resistant to shattering ) . These chilled iron shots proved very effective against wrought iron armor , but were not serviceable against compound and steel armor , which was first introduced in the 1880s . A new departure therefore had to be made , and forged steel rounds with points hardened by water took the place of the Palliser shot . At first , these forged - steel rounds were made of ordinary carbon steel , but as armor improved in quality , the projectiles followed suit . During the 1890s and subsequently , cemented steel armor became commonplace , initially only on the thicker armor of warships . To combat this , the projectile was formed of steel — forged or cast — containing both nickel and chromium . Another change was the introduction of a soft metal cap over the point of the shell – so called " Makarov tips " invented by Russian admiral Stepan Makarov . First World War era . Shot and shell used prior to and during World War I were generally cast from special chromium ( stainless ) steel that was melted in pots . They were forged into shape afterward and then thoroughly annealed , the core bored at the rear and the exterior turned up in a lathe . The projectiles were finished in a similar manner to others described above . The final , or tempering treatment , which gave the required hardness / toughness profile ( differential hardening ) to the projectile body , was a closely guarded secret . The rear cavity of these projectiles was capable of receiving a small bursting charge of about 2 % of the weight of the complete projectile ; when this is used , the projectile is called a shell , not a shot . The HE filling of the shell , whether fuze d or unfuzed , had a tendency to explode on striking armor in excess of its ability to perforate . Second World War . During World War II , projectiles used highly alloyed steels containing nickel - chromium - molybdenum , although in Germany , this had to be changed to a silicon - manganese - chromium - based alloy when those grades became scarce . The latter alloy , although able to be hardened to the same level , was more brittle and had a tendency to shatter on striking highly sloped armor . The shattered shot lowered penetration , or resulted in total penetration failure ; for armor - piercing high - explosive ( APHE ) projectiles , this could result in premature detonation of the HE filling . Highly advanced and precise methods of differentially hardening the projectile were developed during this period , especially by the German armament industry . The resulting projectiles gradually change from high hardness ( low toughness ) at the head to high toughness ( low hardness ) at the rear and were much less likely to fail on impact . APHE shells for tank guns , although used by most forces of this period , were not used by the British . The only British APHE projectile was the " Shell AP , Mk1 " for the 2 pdr anti - tank gun and this was dropped as it was found that the fuze tended to separate from the body during penetration . Even when the fuze didn ’ t separate and the system functioned correctly , damage to the interior was little different from the solid shot , and so did not warrant the additional time and cost of producing a shell version . APHE projectiles of this period used a bursting charge of about 1 – 3 % of the weight of the complete projectile , the filling detonated by a rear mounted delay fuze . The explosive used in APHE projectiles needs to be highly insensitive to shock to prevent premature detonation . The US forces normally used the explosive Explosive D , otherwise known as ammonium picrate , for this purpose . Other combatant forces of the period used various explosives , suitability desensitized ( usually by the use of waxes mixed with the explosive ) . Due to the increase in armor thickness during the conflict , the projectiles ’ impact velocity had to be increased to ensure perforation . At these higher velocities , the hardened tip of the shot or shell has to be protected from the initial impact shock , or risk shattering . To raise the impact velocity and stop the shattering , they were initially fitted with soft steel penetrating caps . The best performance penetrating caps were not very aerodynamic , so an additional ballistic cap was later fitted to reduce drag . The resulting projectile types were named armor - piercing capped ( APC ) and " armor - piercing capped ballistic capped " ( APCBC ) . Early WWII - era uncapped AP projectiles fired from high - velocity guns were able to penetrate about twice their caliber at close range ( 100 m ) . At longer ranges ( 500 - 1 , 000 m ) , this dropped 1 . 5 – 1 . 1 calibers due to the poor ballistic shape and higher drag of the smaller - diameter early projectiles . Later in the conflict , APCBC fired at close range ( 100 m ) from large - caliber , high - velocity guns ( 75 – 128 mm ) were able to penetrate a much greater thickness of armor in relation to their caliber ( 2 . 5 times ) and also a greater thickness ( 2 – 1 . 75 times ) at longer ranges ( 1 , 500 – 2 , 000 m ) . Tungsten compounds such as tungsten carbide were used in small quantities of inhomogeneous and discarded sabot shot , but that element was in short supply in most places . Modern day . Armor - piercing shot . Armor - piercing " shot " for cannons tend to combine some form of incendiary capability with that of armor - penetration . The incendiary compound is normally contained between the cap and penetrating nose , within a hollow at the rear , or a combination of both . If the projectile also uses a tracer , the rear cavity is often used to house the tracer compound . For larger - caliber projectiles , the tracer may instead be contained within an extension of the rear sealing plug . Common abbreviations for solid ( non - composite / hardcore ) cannon - fired shot are ; AP , AP - T , API and API - T ; where " T " stands for " tracer " and " I " for " incendiary " Armor - piercing shells . Armor - piercing shells in the classic form are not common in modern guns , though they may be found in the larger ( 40 – 57 mm ) weapons , especially those of Russian - or Soviet - era descent . Modern guns instead fire semi - armor - piercing high - explosive ( SAPHE ) shells , which have less anti - armor capability , but far greater anti - materiel / personnel effects . The modern SAPHE projectiles still have a ballistic cap , hardened body and base fuze , but tend to have a far thinner body material and higher explosive content ( 4 – 15 % ) . Common abbreviations for modern AP and SAP shells are : HEI ( BF ) , SAPHE , SAPHEI , and SAPHEI - T . Most modern active protection systems ( APS ) are unlikely to be able to defeat full - caliber AP rounds fired from a large - caliber tank gun , due to the high mass of the shot , its rigidity , short overall length , and thick body . The APS uses fragmentation warheads or projected plates , and both are designed to defeat the two most common anti - armor projectiles in use today : HEAT and kinetic energy penetrator . The defeat of HEAT projectiles is accomplished through damage / detonation of the HEAT ' s explosive filling or damage to the shaped charge liner or fuzing system , and defeat of kinetic energy projectiles is accomplished by inducing yaw / pitch or fracturing of the rod . Small arms . Armor - piercing rifle and pistol cartridges are usually built around a penetrator of hardened steel , tungsten , or tungsten carbide , and such cartridges are often called ' hard - core bullets ' . Aircraft and tank rounds sometimes use a core of depleted uranium . The penetrator is a pointed mass of high - density material that is designed to retain its shape and carry the maximum possible amount of energy as deeply as possible into the target . Depleted - uranium penetrators have the advantage of being pyrophoric and self - sharpening on impact , resulting in intense heat and energy focused on a minimal area of the target ' s armor . Some rounds also use explosive or incendiary tips to aid in the penetration of thicker armor . High Explosive Incendiary / Armor Piercing Ammunition combines a tungsten carbide penetrator with an incendiary and explosive tip . Rifle armor - piercing ammunition generally carries its hardened penetrator within a copper or cupronickel jacket , similar to the jacket which would surround lead in a conventional projectile . Upon impact on a hard target , the copper case is destroyed , but the penetrator continues its motion and penetrates the target . Armor - piercing ammunition for pistols has also been developed and uses a design similar to the rifle ammunition . The entire projectile is not normally made of the same material as the penetrator because the physical characteristics that make a good penetrator ( i . e . extremely tough , hard metal ) make the material equally harmful to the barrel of the gun firing the cartridge . Teflon ( polytetrafluoroethylene ) coating on bullets does not help the deep penetration , rather it is to reduce the wear of the barrel caused by hardened projectiles , to reduce the likelihood of a ricochet and decrease deflection when striking glass or plywood .