Editing Armour-piercing ammunition (section)

=== 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}}