Body armor toughness comes in a bunch of different flavors. Over here in the US, we have a couple standards. There’s the National Institute of Justice (NIJ) standards, standards used by the US military, plus a bunch of other marketing-speak. Let’s break it down.

First, NIJ:

NIJ ratings are commonly used for armor marketed to law enforcement and civilians. Some notes:

• All velocities listed above are approximate, and should be understood to be +/- 30 fps.
• Level II and IIIA are soft armor, and are understood to be reasonably multihit.
• Level III and IV are hard plate armor.
• Level IV is required to be able to withstand at least one round of 7.62x51mm M80 FMJ. It is not required to meet Level III multihit standards (6 shots) against M80.
• You may notice there is no testing required against SCHV rounds (e.g. 5.56x45mm, 5.45x39mm). Level III armors may or may not stop SCHV rounds. Level IV armors are required to stop at least one SCHV round.

This last point leads lots of manufacturers to test against various SCHV (usually 5.56mm in the States) rounds, which is good. Do note that “Level III+” and “Level III++” are not NIJ certifications. Those are marketing nonsense. Read the list of test rounds carefully. Some materials used for Level III plates have problems with M855 steel-core (semi-armor piercing) rounds, and some other materials used in Level III plates have problems with the speed of M153 rounds, especially out of a 20″ barrel. Ideally, your plate will withstand both.

What about military plates? I can only speak for the US plates at present. These plates are made from ceramic materials. The US Military uses its own testing standard, not the NIJ one. SAPI¹ plates are designed to resist three hits of “up to” M80 7.62x51mm ball. There’s also ESAPI², which has a similar multihit standard against M2 .30-06 AP rounds. And then there’s XSAPI. Because somewhere out there, some terrorist has some exotic high power super armor piercing 7.62x54R mm that will punch through ESAPI plates and we need to stop that round too. It’s also multihit. Against something exotic, but I don’t know the test round. Maybe tungsten-cored .30-06?

Anyway, as you’d expect, more protection means more weight:

Do note that all US Military plates assume they are mounted over the OTV, IOTV, or equivalent military-spec soft armor for them to perform as advertised. To the best I am able to determine, XSAPI plates have never been deployed in combat. They sit in depots because they’re too damn heavy and because the expected threat never materialized. Also, remember the above is per plate. Double it.

That military soft armor is tested to a different standard than the NIJ one. The military is concerned with fragmentation, primarily, so they look at the V₅₀, i.e. the speed at which a given projectile must be going to have a 50% chance of penetration. This number is chosen because it’s a lot easier to work with than V₀ from a measurements and statistics perspective. To simulate artillery fragments, the US Army tests with steel projectiles with weights of 2, 4, 16, and 64 grains. Steel doesn’t deform like lead pistol bullets do, so this is sort of a different challenge than regular pistol bullets. The V₅₀ for a 124 grain 9mm NATO round against the current soft armor in the IOTV is about 1,525 fps, which is pretty similar to that of most Level IIIA soft armor panels. On the other hand, the NIJ requires Level IIIA panels to also stop .44 magnum rounds, and the US Military doesn’t.

Next time, we’ll take a more in-depth look at soft body armor systems.