If you’ve heard the term “armor-piercing ammunition” on the news, it would be no surprised if you’re confused about what it actually means—between the mainstream media’s general ignorance and simultaneous hysterical fear of firearms, the term gets misused and misunderstood (especially when they’re called by the inflammatory nickname “cop killers”). Ignorant politicians sometimes call ammunition "armor piercing" when it's really not. So what are armor-piercing bullets, exactly?
Simply put, they’re just what they sound like: projectiles designed to penetrate barriers like steel, ceramic, bulletproof glass, body armor and more. While FMJ and hollowpoint ammunition typically use bullet cores made of lead, a relatively soft and malleable metal, armor-piercing (AP) rounds use projectiles that include hardened steel, tungsten carbide or other harder metal. Some use a lead core wrapped in a steel jacket.
They come in many types and are intended to shoot through armored vehicles, “bulletproof” vests, and even tanks. As you might imagine, this is pretty much limited to military and law enforcement uses, and in the U.S., it is illegal to sell armor-piercing handgun rounds to civilians. On a federal level, most armor-piercing rifle ammunition is not subject to the same restrictions, but many states prohibit civilians from owning it.
Legally speaking, the term “armor piercing” refers to handgun ammo, or bullets that “may be used” in a handgun—a definition that has muddied the waters a bit with the advent of AR-15 and other large-format pistols. As for rifle ammo, some common full metal jacket (FMJ) rifle rounds are already capable of piercing armor just by the way they’re built, but there are also brands that make specialized armor-piercing rifle ammo for military use. These rounds are often distinguishable by their tips.
This is a mostly moot discussion, as you won’t likely be buying any AP ammo anytime soon, but just for your education, as with most things in life, AP ammo comes with a trade-off. Projectiles are generally designed to be good at destroying one of two things: Hard stuff (like steel) or soft stuff (like flesh for hunting or personal defense). If they’re good at one, they won’t be very good at the other. This is why hollowpoint rounds, designed to expand when they hit something, excel at making devastating wound channels in tissue but can’t penetrate a hard surface or barrier. At the same time, AP rounds are designed to punch through harder stuff, but they also zip right through tissue relatively cleanly, making them less effective for self-defense. The military uses AP rounds to take out hardened targets that are hiding behind or inside a barrier.
So that’s the basics: Armor-piercing rounds have a hard core or a hard jacket that enables them to penetrate barriers that most "normal" ammunition can’t go through. Different levels of AP ammo exist, as do different levels of body armor. They are generally for specialty military and law enforcement use. In general, civilians have little practical application for AP rounds and cannot be sold AP handgun rounds at all.
