Armor-piercing round

Armor Piercing Rounds, alternately spelled as Armour Piercing Rounds (UK Spelling) and colloquially known as AP rounds, are the type of ammo used in most small arms weapons like Assault Rifles used by the United Nations Space Command. When all the AP rounds in a weapon are used up, some personnel switch to Shredder Rounds, as the SPARTANs of Blue Team did on a mission in the Lambda Serpentis System. The SRS99C-S2 AM Sniper Rifle's bullets are armor piercing as well.

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 it's energy directly into the target, causing massive trauma and kinetic energy damage. The downside of AP rounds is that they perform poorly against energy shielding.