Rifle armor-piercing ammunition generally carries its hardened penetrator within a copper or cupronickel jacket, similar to the jacket which would surround lead in a conventional projectile. Upon impact on a hard target, the copper case is destroyed, but the penetrator continues its motion and penetrates the target.

Why is armor-piercing rounds illegal?

This is because this law was adopted as part of the Law Enforcement Officer's Safety Act and was intended to regulate “cop-killer” bullets from easily concealable firearms (handguns).

How do armor-piercing incendiary rounds work?

The special effect is developed when the round strikes the target. The initial collision ignites the incendiary material in the tip, triggering the detonation of the HE charge. The second (zirconium powder) incendiary charge will also ignite. ... The remaining element of the round is the tungsten carbide penetrator.