Let’s start with some basics regarding armor –

First, there are two basic categories of armor: body armor and
structual armor. When the military designates a particular type of
ammo “armor piercing”, they are refering to structual armor such as
might be found on a vehicle or fighting position. Usually this is
hard metallic armor. Body armor is what is worn by people and often
defeats projectiles in a much different fashion than structual armor
and is often fabric based. Body armor (in the US) is divided into
levels by the military and National Institute of Justice. The
military “flak jacket” is designed to stop shrapnel from grenades and
other explosives. Flak jackets were not designed to stop bullets.
NIJ Levels I, IIa, II, and IIIa are all designed to stop handgun ammo
such as .22s, .38s, 9mm, .357s, .44s amd .45s. The ratings are in
ascending order of protection. None of these levels are rated for
rifle projectiles. Onle NIJ Levels III and IV are rated against
rifles, with level III rated against less powerful ammo such as that
fired by the AK-47 and M-16 while Level IV is rated against more
powerful rifles and some military rated AP ammo. Many none AP
“hunting rifles” will defeat Level IV body armor.

The military usually designates a type of ammo as “AP” if it can
defeat a specific level of hard steel armor at a certain distance
(such as 13mm of steel at 100 meters). The military does not
recognize any AP rating for any handgun ammo. Handgun ammo generally
lacks the velocity and sectional density to be “armor piercing”.

Enter the FN 5.7mm ammo. This ammo was a kind of hybrid ammo similar
to the .224 BOZ envisioned to bridge the gap between handgun ammo and
rifle ammo. Basically, these are downloaded (less powerful) versions
of the 5.56×45mm NATO ammo used in the M-16. The original idea was to
give special units handgun ammo which could defeat the Soviet CRISAT
body armor better than a 9mm could. Lack of velocity remained an
issue when fired from handguns, so a new concept called a PDW
(Personal Defense Weapon) was developed. Essentially a PDW was a
sub-machine gun type platform. With its longer barrel, the PDW could
get enough velocity to be effective against CRISAT body armor. FN’s
5.7mm PDW is called the P90. If you watched the Stargate SG1 TV
series, they routinely carried the P90 (or the PS90 civilian version
which will not fire full-auto). Even in the P90, the 5.7mm was less
effective than 5.56×45mm NATO ammo and its only advantage over the
5.56 was it was slightly shorter and lighter, making it easier to
carry more ammo. Therefore, most militaries around the world realized
this was a solution looking for a problem and did not purchase it.

The 5.7mm ammo original load was the SS90 which, out of the P90 had a
modest velocity of around 853 meters per second (many hunting rifles
run 944 m/s or faster and the 5.56 runs upward of 944 m/s with a
projectile the same diameter and twice as heavy as the SS90). This
was supposed to defeat the CRISAT body armor, but it could not garner
a military AP rating. The SS90 would not correctly work in the
Five-seveN pistol, reducing it to single shot action with manual
reload. The SS190 was introduced to be universally compatible with
the P90 carbine and the Five-seveN pistol, but even out of the P90
only had a lackluster velocity of 716 m/s, which put it in the same
kinteic energy power range as most 9mm ammo (fired from a pistol).
Out of the Five-seveN pistol, with its shorter barrel, the SS190 was
even less powerful with a velocity of about 650 m/s.

When fired from a Five-seveN pistol, even the most potent 5.7mm ammo
could only defeat NIJ Level IIa body armor, one of the lowest
protection levels of body armor. Many 9mm loads are capable of doing
this. Regardless, in the US the government restricted sales of some
types of 5.7mm ammo and those particular types are not sold
commercially.

When it comes to terminal performance, extensive testing has shown
that the 5.7mm bullets, especially when hitting at less than 792 m/s,
do not perform well. Any decent 9mm hollow point is far more
devastating.

The bottom line is that the 5.7mm ammo and the Five-seveN pistol are
not AP rated and are rather lack luster performers despite the hype
surrounding them. There is little the 5.7mm and Five-seveN can do
that a common 9mm will not.

As crass as it sounds, people were lucky that the shooter believed the
hype and chose the Five-seveN and not a standard 9mm like a Glock,
Beretta, Walther, etc. Had he chosen a 9mm, more people would
probably have died.

v/r

Dave H.
Deputy Sheriff
Law enforcement and civilian arms instructor
Certified law enforcement armorer
Retired military combat veteran and former military arms instructor