Armor-piercing, capped, ballistic capped shell
Armor-piercing, capped, ballistic capped (APCBC) is a type of armor-piercing shell configuration introduced in the 1930s to improve the armor-piercing capabilities of both naval and anti-tank guns. The configuration consists of a basic armor-piercing shell, normally an armor-piercing high explosive shell, fitted with a soft metal cap on its tip, normally with a blunt shape, and a hollow cone made out of thin metal on top of the cap, formally named ballistic cap.
The job of the soft metal cap is to protect the tip of the penetrator on impact and to help guide the projectile into the armor at high impact angles by gripping into the armor and acting a bit like glue through the properties of soft metal.
The job of the ballistic cap is to give the projectile a more aerodynamic shape to increase velocity and range, which in turn increases maximum penetration and penetration over range. On impact, the ballistic cap will break off or be crushed so as to not impact the performance of the regular cap and penetrator.
These features allow APCBC shells to retain higher velocities and to deliver more energy to the target on impact, especially at long range when compared to uncapped shells.