Editing Armour-piercing ammunition (section)

== Armour-piercing solid shots ==
Armour-piercing solid shot for cannons may be simple, or composite, solid projectiles but tend to also combine some form of incendiary capability with that of armour-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 ammunition|tracer]], the rear cavity is often used to house the tracer compound. For larger-calibre 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". More complex, composite projectiles containing explosives and other ballistic devices tend to be referred to as armour-piercing shells.

=== AP ===
Early WWII-era uncapped ''armour-piercing'' (''AP'') projectiles fired from high-velocity guns were able to penetrate about twice their calibre at close range (100&nbsp;m). At longer ranges (500–1,000&nbsp;m), this dropped 1.5–1.1 calibres due to the poor ballistic shape and higher drag of the smaller-diameter early projectiles. In January 1942 a process was developed by Arthur E. Schnell<ref>Western Hills Press, Cheviot Ohio Page 3-B May 30th 1968</ref> for 20&nbsp;mm and 37&nbsp;mm armour piercing rounds to press bar steel under 500 tons of pressure that made more even "flow-lines" on the tapered nose of the projectile, which allowed the shell to follow a more direct nose first path to the armour target.  Later in the conflict, APCBC fired at close range (100&nbsp;m) from large-calibre, high-velocity guns (75–128&nbsp;mm) were able to penetrate a much greater thickness of armour in relation to their calibre (2.5 times) and also a greater thickness (2–1.75 times) at longer ranges (1,500–2,000&nbsp;m).

In an effort to gain better aerodynamics, AP rounds were given [[ballistic cap]]s to reduce drag and improve impact velocities at medium to long range.  The hollow ballistic cap would break away when the projectile hit the target. These rounds were classified as armour-piercing ballistic capped (APBC) rounds.

Armour-piercing, capped projectiles had been developed in the early 1900s, and were in service with both the British and German fleets during World War I. The shells generally consisted of a [[nickel steel]] body that contained the burster charge and was fitted with a hardened steel nose intended to penetrate heavy armour. Striking a hardened steel plate at high velocity imparted significant force to the projectile and standard armour-piercing shells had a tendency to shatter instead of penetrating, especially at oblique angles, so shell designers added a [[mild steel]] cap to the nose of the shells. The more flexible mild steel would deform on impact and reduce the shock transmitted to the projectile body. Shell design varied, with some fitted with hollow caps and others with solid ones.<ref>{{cite book|last=Brooks|first=John|title=The Battle of Jutland|year=2016|location=Cambridge|publisher=Cambridge University Press|pages=76–79, 90|isbn=9781107150140}}</ref>

Since the best-performance penetrating caps were not very aerodynamic, an additional [[ballistic cap]] was later fitted to reduce drag. The resulting rounds were classified as armour-piercing capped ballistic capped (APCBC). The hollow ballistic cap gave the rounds a sharper point which reduced drag and broke away on impact.<ref name="books.google.com">[https://books.google.com/books?id=4CEDAAAAMBAJ&pg=PA122 Popular Science, December 1944, pg 126] illustration at bottom of page on working principle of APCBC type shell</ref>

=== SAP ===
{{Further|Glossary of British ordnance terms#S.A.P.}}''Semi-armour-piercing'' (''SAP'') shot is a solid shot made of [[mild steel]] (instead of [[high-carbon steel]] in AP shot). They act as low-cost ammunition with worse penetration characteristics to contemporary high carbon steel projectiles.
{{Expand section|date=November 2023}}<!--SAP is likely different from SAPHE, i.e. not a short hand. However the linked page mentions SAP contains explosives, which may not necessarily be the case, SAP is likely a shot made from softer material with no explosive-->

=== APCR/HVAP ===
''Armour-piercing composite rigid'' (''APCR'') in British [[nomenclature]], ''high-velocity armour-piercing'' ('''HVAP''') in US nomenclature, alternatively called "hard core projectile" ({{langx|de|Hartkernprojektil}}) or simply "core projectile" ({{langx|sv|kärnprojektil}}), is a projectile which has a core of high-density hard material, such as [[tungsten carbide]], surrounded by a full-bore shell of a lighter material (e.g., an [[aluminium]] alloy). However, the low [[sectional density]] of the APCR resulted in high [[aerodynamic drag]]. Tungsten compounds such as tungsten carbide were used in small quantities of inhomogeneous and discarded sabot round, but that element was in short supply in most places. Most APCR projectiles are shaped like the standard APCBC round (although some of the German ''Pzgr.'' 40 and some Soviet designs resemble stubby arrows), but the projectile is lighter: up to half the weight of a standard AP round of the same calibre. The lighter weight allows a higher muzzle velocity. The kinetic energy of the round is concentrated in the core and hence on a smaller impact area, improving the penetration of the target armour. To prevent shattering on impact, a shock-buffering cap is placed between the core and the outer ballistic shell as with APC rounds. However, because the round is lighter but still the same overall size it has poorer ballistic qualities, and loses velocity and accuracy at longer ranges. The APCR was superseded by the APDS, which dispensed with the outer light alloy shell once the round had left the barrel. The concept of a heavy, small-diameter penetrator encased in light metal was later employed in small-arms armour-piercing incendiary and HEIAP rounds.

=== APCNR/APSV ===
{{Main|Squeeze bore}}
{{further|Littlejohn adaptor|2.8 cm sPzB 41|7.5 cm Pak 41}}
[[File:APBCT (cropped).jpg|thumb|German Armour-Piercing, Composite Non-Rigid projectile]]

''Armour-piercing, composite non-rigid'' (''APCNR'') in British [[nomenclature]],{{efn|In case of the british [[Littlejohn adaptor]], ammunition was designated as ''armour-piercing, super-velocity'' (''APSV'').}} alternatively called "flange projectile" ({{langx|sv|flänsprojektil}}) or less commonly "armour-piercing super-velocity", is a [[sub-calibre]] projectile used in [[squeeze bore]] weapons (also known as "tapered bore" weapons) – weapons featuring a barrel or barrel extension which taperes towards the muzzle – a system known as the [[Gerlich principle]]. This projectile design is very similar to the APCR-design - featuring a high-density core within a shell of soft iron or another alloy - but with the addition of soft metal [[flange]]s or studs along the outer projectile wall to increase the projectile diameter to a higher caliber. This caliber is the initial full-bore caliber, but the outer shell is deformed as it passes through the taper. Flanges or studs are swaged down in the tapered section so that as it leaves the muzzle the projectile has a smaller overall cross-section.<ref name="books.google.com"/> This gives it better flight characteristics with a higher sectional density, and the projectile retains velocity better at longer ranges than an undeformed shell of the same weight. As with the APCR, the kinetic energy of the round is concentrated at the core of impact. The initial velocity of the round is greatly increased by the decrease of barrel cross-sectional area toward the muzzle, resulting in a commensurate increase in velocity of the expanding propellant gases.

The Germans deployed their initial design as a light anti-tank weapon, ''[[2.8 cm sPzB 41|2.8 cm schwere Panzerbüchse 41]]'', early in [[World War II]], and followed by the [[4.2 cm Pak 41]] and [[7.5 cm Pak 41]]. Although HE rounds were also put into service, they weighed only 93&nbsp;grams and had low effectiveness.<ref>{{cite book |last=Shirokorad |first=A. B. (Широкорад А. Б.) |year=2002 |title=The God of War of the Third Reich (Бог войны Третьего рейха) |publisher=M. AST (М.,ООО Издательство АСТ) |isbn=978-5-17-015302-2}}</ref> The German taper was a fixed part of the barrel.

In contrast, the British used the [[Littlejohn adaptor|Littlejohn squeeze-bore adaptor]], which could be attached or removed as necessary. The adaptor extended the usefulness of armoured cars and light tanks, which could not be upgraded with any gun larger than the QF 2 pdr. Although a full range of shells and shot could be used, changing an adaptor during a battle is usually impractical.

The APCNR was superseded by the APDS design which was compatible with non-tapered barrels.

=== APDS ===
{{Main|armour-piercing discarding sabot}}
[[File:24 mm slpprj m49.png|thumb|Swedish armour-piercing discarding sabot projectile, here seen with and without its [[Sabot (firearms)|sabot]] as well as its internal [[tungsten]] core]]
An important armour-piercing development was the ''armour-piercing discarding [[Sabot (firearms)|sabot]]'' (''APDS''). An early version was developed by engineers working for the French [[Edgar Brandt|Edgar Brandt company]], and was fielded in two calibres (75&nbsp;mm/57&nbsp;mm for the [[Canon de 75 modèle 1897|75 mm Mle1897/33 anti-tank gun]], 37&nbsp;mm/25&nbsp;mm for several 37&nbsp;mm gun types) just before the French-German armistice of 1940.<ref>{{cite web|url=http://www.museumoftechnology.org.uk/military.php?cab=shells|title=Shells and Grenades|publisher=The Museum of Technology|location=Old Town, Hemel Hempstead|access-date=2010-10-23| archive-url= https://web.archive.org/web/20101016002149/http://www.museumoftechnology.org.uk/military.php?cab=shells| archive-date= 16 October 2010 | url-status= live}}</ref> The Edgar Brandt engineers, having been evacuated to the United Kingdom, joined ongoing APDS development efforts there, culminating in significant improvements to the concept and its realization.  The APDS projectile type was further developed in the United Kingdom between 1941 and 1944 by L. Permutter and S. W. Coppock, two designers with the Armaments Research Department. In mid-1944 the APDS projectile was first introduced into service for the UK's [[Ordnance QF 6-pounder|QF 6-pdr]] [[anti-tank gun]] and later in September 1944 for the [[Ordnance QF 17-pounder|QF-17 pdr]] anti-tank gun.<ref>{{cite web|url=http://www.avalanchepress.com/17-Pounder.php|title=The 17-Pounder|author=Jason Rahman|publisher=Avalanche Press|date=February 2008|access-date=2010-10-23| archive-url= https://web.archive.org/web/20101109112825/http://www.avalanchepress.com/17-Pounder.php| archive-date= 9 November 2010 | url-status= live}}</ref> The idea was to use a stronger and denser penetrator material with smaller size and hence less drag, to allow increased impact velocity and armour penetration.

The armour-piercing concept calls for more penetration capability than the target's armour thickness. 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. Generally, the penetration capability of an armour-piercing round increases with the projectile's kinetic energy, and with concentration of that energy in a small area. Thus, an efficient means of achieving increased penetrating power is increased velocity for the projectile. However, projectile impact against armour at higher velocity causes greater levels of shock. Materials have characteristic maximum levels of shock capacity, beyond which they may shatter, or otherwise disintegrate. At relatively high impact velocities, steel is no longer an adequate material for armour-piercing rounds. Tungsten and tungsten alloys are suitable for use in even higher-velocity armour-piercing rounds, due to their very high shock tolerance and shatter resistance, and to their high melting and boiling temperatures. They also have very high density. Aircraft and tank rounds sometimes use a core of [[depleted uranium]]. Depleted-uranium penetrators have the advantage of being [[Pyrophoricity|pyrophoric]] and self-sharpening on impact, resulting in intense heat and energy focused on a minimal area of the target's armour. Some rounds also use [[Explosive material|explosive]] or [[Incendiary device|incendiary]] tips to aid in the penetration of thicker armour. [[High-explosive incendiary/armor-piercing ammunition|High explosive incendiary/armour piercing ammunition]] combines a [[tungsten carbide]] penetrator with an incendiary and explosive tip.

Energy is concentrated by using a reduced-diameter tungsten shot, surrounded by a lightweight outer carrier, the ''sabot'' (a French word for [[Sabot (shoe)|a wooden shoe]]). This combination allows the firing of a smaller diameter (thus lower mass/aerodynamic resistance/penetration resistance) projectile with a larger area of expanding-propellant "push", thus a greater propelling force and resulting kinetic energy. Once outside the barrel, the sabot is stripped off by a combination of [[centrifugal force]] and aerodynamic force, giving the shot low drag in flight. For a given calibre, the use of APDS ammunition can effectively double the anti-tank performance of a gun.

=== APFSDS ===
{{Main|Armour-piercing fin-stabilized discarding sabot}}
[[File:Obus-flèche français OFL 105 F1.jpg|thumb|French armour-piercing, fin-stabilized, discarding sabot projectile]]

''Armour-piercing fin-stabilized discarding sabot'' (''APFSDS'') in English [[nomenclature]], alternatively called "arrow projectile" or "dart projectile" ({{langx|de|Pfeil-Geschoss}}, {{langx|sv|pilprojektil}}, {{langx|no|pilprosjektil}}), is a [[saboted]] [[sub-calibre]] [[Sectional density|high-sectional density]] projectile, typically known as a [[long rod penetrator]] (LRP), which has been outfitted with fixed fins at the back end for ballistic-stabilization (so called aerodynamic drag stabilization). The fin-stabilisation allows the APFSDS sub-projectiles to be much longer in relation to its sub-calibre thickness compared to the very similar spin-stabilized ammunition type APDS (armour-piercing discarding sabot). Projectiles using spin-stabilization ([[Angular momentum#Conservation of angular momentum|longitudinal axis rotation]]) requires a certain mass-ratio between length and diameter (calibre) for accurate flight, traditionally a length-to-diameter ratio less than 10{{citation needed|date=August 2012}} (more for higher density projectiles).{{citation needed|date=August 2012}} If a spin-stabilized projectile is made too long it will become unstable and tumble during flight. This limits how long APDS sub-projectiles of can be in relation to its sub-calibre, which in turn limits how thin the sub-projectile can be without making the projectile mass too light for sufficient [[kinetic energy]] (range and penetration), which in turn limits how [[aerodynamic]] the projectile can be (smaller calibre means less [[air-resistance]]), thus limiting [[velocity]], etc., etc. To get away from this, APFSDS sub-projectiles instead use aerodynamic drag stabilization (no longitudinal axis rotation), by means of fins attached to the base of the sub-projectile, making it look like a large metal arrow. APFSDS sub-projectiles can thus achieve much higher length-to-diameter ratios than APDS-projectiles, which in turn allows for much higher sub-calibre ratios (smaller sub-calibre to the full-calibre), meaning that APFSDS-projectiles can have an extremely small frontal cross-section to decrease [[air-resistance]], thus increasing [[velocity]], while still having a long body to retain great mass by length, meaning more [[kinetic energy]]. Velocity and kinetic energy both dictates how much range and penetration the projectile will have. This long thin shape also has increased [[sectional density]], in turn increasing penetration potential.

Large calibre (105+ mm) APFSDS projectiles are usually fired from [[smoothbore]] (unrifled) barrels, as the fin-stabilization negates the need for spin-stabilization through [[rifling]]. Basic APFSDS projectiles can traditionally not be fired from rifled guns, as the immense spinning caused by the rifling damages and destroys the fins of the projectile, etc. This can however be solved by the use of "slipping driving bands" on the [[Sabot (firearms)|sabot]] ([[driving band]]s which rotates freely from the sabot). Such ammunition was introduced during the 1970s and 1980s for rifled high-calibre tank guns and similar, such as the Western [[Royal Ordnance L7]] and the Eastern [[D-10T]].<ref>{{cite book |last1=Ogorkiewicz |first1=Richard M |title=Technology of tanks |pages=76 |date=1991 |publisher=Jane's Information Group }}</ref> However, as such guns have been taken out of service since the early 2000s onwards, rifled APFSDS mainly exist for small- to medium-calibre (under 60&nbsp;mm) weapon systems, as such mainly fire conventional full-calibre ammunition and thus need rifling.

APFSDS projectiles are usually made from high-density metal alloys, such as [[tungsten]] heavy alloys (WHA) or [[depleted uranium]] (DU); [[maraging steel]] was used for some early Soviet projectiles. DU alloys are cheaper and have better penetration than others, as they are denser and self-sharpening. Uranium is also [[pyrophoric]] and may become opportunistically incendiary, especially as the round [[adiabatic shear band|shears]] past the armour exposing non-oxidized metal, but both the metal's fragments and dust contaminate the battlefield with toxic hazards. The less toxic WHAs are preferred in most countries except the US and Russia.{{Citation needed|date=June 2011}}