Armor Piercing Incendiary
Armor piercing incendiary ammo is an ammo type that is meant to pierce armor and also set materiel on fire. In addition to setting things on fire the incendiary also serves to show the gunner where they hit by the flash of the impact.
The common design is a hard steel or tungsten core, with a copper jacket, a lead base, and incendiary filler in the tip in front of the base and core.
The US military ISAPI(Improved Small Arms Protective Inserts) armor standard was meant to stop API threats in Iraq however ISAPI was superceded by ESAPI(Enhanced Small Arms Protective Inserts) before it was widely issued.
It is not a war crime unless used where fire could spread to areas with civilians.
Varieties include HEIAP(High Explosive Incendiary Armor Piercing) rounds such as the Raufoss Mk 211. These also contain a high explosive in addition to the incendiary.
Depending on the composition, the incendiary may fail to ignite on impacting soft targets such as people.