The rounds that penetrate body armor depend almost entirely on what level of armor you’re talking about. Soft body armor worn by police officers stops most handgun rounds but is easily defeated by nearly any rifle cartridge. Hard armor plates rated for rifles stop common threats like 7.62x51mm NATO, but certain high-velocity or armor-piercing rounds can punch through even those. Level IV ceramic plates, the highest standard available, stop armor-piercing .30-06 and most other threats short of heavy anti-materiel rounds.
How Armor Protection Levels Work
The National Institute of Justice sets the testing standards for body armor sold in the United States. Each protection level is tested against specific rounds at specific velocities, and anything more powerful than the test threat has a real chance of getting through. The system was recently updated with new naming conventions: the old Level II is now HG1, Level IIIA is HG2, Level III is RF1, and Level IV is RF3. A new intermediate rifle level, RF2, was also introduced.
These ratings tell you the minimum a plate must stop, not the maximum. Many manufacturers build plates that exceed their rated level. But the ratings remain the clearest way to understand which rounds pose a threat to which armor.
What Soft Armor Stops and What Gets Through
Soft body armor, the flexible panels worn under or over clothing, is designed to defeat handgun rounds. Level II (HG1) armor is tested against 9mm at 1,305 feet per second and .357 Magnum at 1,430 feet per second. Level IIIA (HG2) armor handles hotter loads: 9mm at 1,470 feet per second and .44 Magnum at 1,430 feet per second. In practice, IIIA armor stops most common handgun calibers on the market, from .380 ACP up through .44 Magnum.
What soft armor cannot stop is rifle fire. Even a basic .223 Remington or 5.56mm NATO round from an AR-15 will punch straight through Level IIIA panels. The difference comes down to velocity. Handgun rounds typically travel between 800 and 1,500 feet per second. Rifle rounds travel at 2,400 to 3,200 feet per second or faster, and that energy concentrated on a small, fast-moving projectile overwhelms the flexible fibers in soft armor.
Rifle Rounds That Defeat Level III Plates
Level III (RF1) hard armor plates are tested against three rifle threats: 7.62x51mm M80 ball at 2,780 feet per second, 7.62x39mm at 2,400 feet per second, and 5.56mm M193 at 3,250 feet per second. A plate that passes this test will stop standard-issue AK-47 and AR-15 ammunition along with full-power .308 Winchester ball rounds.
Here’s where it gets counterintuitive. Several rounds that are smaller or seem less powerful than .308 can actually defeat Level III plates. The XM193 round fired from a longer barrel at close range generates enough velocity to pierce many Level III standalone plates, particularly those made from steel. The M855 “green tip” 5.56mm round, with its steel penetrator tip, poses problems for certain plate materials. And the newer M855A1 Enhanced Performance Round, now standard issue for the U.S. military, defeats AR500 steel plates at close range and has also penetrated some ceramic composite Level III+ plates at short distances.
Other rounds that can punch through Level III armor include .338 Lapua Magnum and various .223 loads with steel or tungsten penetrators. The key point is that a bigger bullet doesn’t necessarily mean better armor penetration. A lightweight, fast round with a hard core often outperforms a larger, slower projectile.
What It Takes to Beat Level IV
Level IV (RF3) is the highest NIJ-rated protection, tested against .30-06 M2 armor-piercing rounds at 2,880 feet per second. This is a full-power rifle cartridge with a hardened steel core specifically designed to defeat armor. Quality Level IV plates, typically built from alumina oxide ceramic bonded to a polyethylene composite backing, can also stop M855A1, 7.62x54R (the standard Russian machine gun round), and in some cases even .338 Lapua Magnum.
Defeating Level IV requires either exotic ammunition or substantially more powerful cartridges. Rounds using tungsten carbide cores offer significantly better penetration than traditional hardened steel cores, even when carrying less total energy. Tungsten carbide is nearly twice as dense as steel and far harder, allowing it to concentrate force on a smaller area and push through ceramic strike faces more effectively. Military research into converting standard 7.62x51mm armor-piercing rounds to tungsten carbide cores has shown improved penetration despite lower impact energy overall.
Beyond specialty small arms, anti-materiel rifles chambered in .50 BMG or 14.5x114mm generate so much energy that standard Level IV body armor plates are not designed or rated to stop them.
Why Bullet Design Matters More Than Caliber
The three factors that determine whether a round penetrates armor are velocity, core hardness, and projectile shape. A round doesn’t need to be large if it’s fast and hard. This is why a 5.56mm M855A1, weighing only 62 grains, can defeat steel plates that comfortably stop a 147-grain 7.62mm ball round.
Armor-piercing projectiles work by concentrating force through a small, extremely hard penetrator. The outer jacket, usually brass, strips away on impact and plays almost no role in the penetration itself. What matters is the core. Standard ball ammunition uses a lead core, which deforms on impact and spreads its energy across the armor surface. Armor-piercing rounds replace that lead with hardened steel, tungsten carbide, or in some military applications, depleted uranium. These materials resist deformation, maintaining a sharp profile that digs into and through armor plate.
Velocity plays an equally important role. The same round that bounces off a steel plate at 200 yards may punch through it at 25 yards, simply because it hasn’t lost speed to air resistance yet. This is why manufacturer testing distance matters enormously for real-world performance.
The “Level III+” Gap
One of the most important things to understand is that Level III+ is not an official NIJ designation. It’s a manufacturer label indicating that a plate exceeds Level III but hasn’t been tested to Level IV standards. Plates marketed as III+ typically claim to stop M193, M855, and sometimes M855A1 in addition to the standard Level III test threats.
This matters because someone wearing a standard Level III plate may assume they’re protected against AR-15 fire when, depending on the specific ammunition used, they may not be. If protection against 5.56mm threats is a priority, look for plates specifically tested against M193 and M855 at realistic distances rather than relying on the Level III rating alone. Some newer III+ plates have been engineered to stop M855A1 at distances as close as 25 yards, but earlier generations of the same product line failed against that round.
How Federal Law Defines Armor-Piercing Ammo
Under federal law (18 USC ยง 921), armor-piercing ammunition is defined specifically for handgun rounds. A projectile qualifies if its core is constructed entirely from tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium. Alternatively, any full-jacketed handgun projectile larger than .22 caliber whose jacket makes up more than 25% of the total projectile weight also qualifies. This definition does not cover rifle ammunition, which is why M855 green tip 5.56mm remains legal for civilian purchase despite containing a steel penetrator. The law also exempts shotgun shot used for hunting, frangible target rounds, and projectiles the Attorney General designates for sporting or industrial use.
What Happens When Armor Stops a Round
Even when body armor successfully prevents penetration, the impact transfers significant energy to the wearer. NIJ standards allow a maximum backface deformation of 44mm (about 1.7 inches) in the clay backing used during testing. That deformation translates to blunt force trauma for the person wearing the armor. Broken ribs, severe bruising, and internal injuries are possible even from a stopped round. Hard ceramic plates distribute this force better than soft armor, and multi-curve plates that conform to the body’s shape improve both comfort and performance compared to flat “single-curve” designs.
Ceramic plates also face limitations after taking hits. The ceramic layer cracks on impact by design, as shattering the ceramic is what absorbs and disperses the bullet’s energy. This means the area around an impact site is weakened. Quality Level IV plates are multi-hit rated, meaning they can take several rounds and still provide protection, but the hits need to be spread across the plate’s surface rather than concentrated in one spot.