wait...so it can penetrate armor, yet its not considered armor-piercing?
It's all word games, and it depends on who is writing the words.
In Texas for example, it's only considered "Armor Piercing Ammo" if it can be fired from a handgun. If it's rifle ammo it has no particular legal definition but if you can shoot it in a handgun it is "AP" and illegal to possess. Makes sense huh?
On a Federal level it's defined as: (bold added by me)
The definition of AP ammo is at 18 USC sec. 921(a)(17):
"(B) The term 'armor piercing ammunition' means-
(i) a projectile or projectile core which may be used in a handgun and which is constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium; or
(ii) a full jacketed projectile larger than .22 caliber designed and intended for use in a handgun and whose jacket has a weight of more than 25 percent of the total weight of the projectile.
Now the gotcha of course is the "handgun" stuff. Shotgun shot is made entirely of steel but of course it's not armor piercing.
Another problem is the Feds have said that even stuff like .308 and 5.56 counts because somewhere sometime someone made a handgun that would fire those.
So, M855 is not armor piercing by definition. It has nothing to do with whether or not it will go through different types of armor, it's solely based on construction materials.
An ATF list includes:
All KTW, ARCANE, and THV ammo.
Czech made 9mm Para. with steel core.
German made 9mm Para. with steel core.
MSC .25 ACP with brass bullet.
BLACK STEEL armor and metal piercing ammunition.
7.62mm NATO AP and SLAP.
PMC ULTRAMAG with brass bullet (but not copper).
OMNISHOCK .38 Special with steel core.
7.62x39 ammo with steel core bullets.
ATF specifically excludes:
5.56 SS109 and M855 NATO rounds
.30-06 M2 AP ammo.
And the laws around all this are:
ok to OWN AP ammo
ok to SELL AP ammo
ok to BUY AP ammo
ok to SHOOT AP ammo
NOT ok to MAKE AP ammo (18 USC sec. 922(a)(7))
NOT ok to IMPORT AP ammo (18 USC sec. 922(a)(7))
Also note that if you have an FFL, even a C&R, you must record the sale of AP ammo.
(Most of this from Bardwell)