Armor piercing round

Armor piercing rounds, colloquially known as AP rounds, are the type of ammunition designed to penetrate armor.

Overview
Armor piercing rounds are used to penetrate hardened, armored targets such as ballistic vests, vehicle armor, concrete, tanks, and other defenses, depending on the caliber of the round. AP rounds are tipped with a hard metallic cap. The cap can be made from tungsten, steel, a carbide of some sort, or even depleted uranium. This allows the bullet to pierce through armor, as the projectile stays intact because the tip of the round does not deform enough to slow it down dramatically. Armor piercing ammunition is designed to dump almost all of its energy directly into the target, causing massive trauma and kinetic energy damage.

The disadvantage of AP rounds is that they perform poorly against energy shields, as the shielding defeats the piercing qualities of the bullet. An AP round must thus rely simply upon its kinetic energy to deplete the shields before it can damage the shielded enemy. Large rounds, such as the 12.7x99mm Armor-Piercing and the 14.5x114mm, perform well under these conditions. However, smaller AP rounds, such as the M118 7.62x51mm and the M634 9.5x40mm, are ineffective unless used in large quantities.