Definition of armor piercing from 18 USC 921(a)(17)
(17)(A) The term "ammunition" means ammunition or cartridge cases, primers, bullets, or propellent powder designed for use in any firearm.
(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.
(C) The term "armor piercing ammunition" does not include shotgun shot required by Federal or State environmental or game regulations for hunting purposes, a frangible projectile designed for target shooting, a projectile which the Attorney General finds is primarily intended to be used for sporting purposes, or any other projectile or projectile core which the Attorney General finds is intended to be used for industrial purposes, including a charge used in an oil and gas well perforating device.
What does all that mean?
A few things to take note of is that the classification as "armor piercing" is for bullets only, not the complete cartridge. Despite the mention of handgun caliber above, you can take that to mean that it's a round that has been made as a handgun caliber at some point.
The bullet (projectile) must also have a core made entirely out of the metals listed above, or be a full jacketed bullet with a jacket weighing more than 25% of its overall weight. This means that the SS109/M855 bullets wouldn't be covered, as their cores are partly steel, and partly lead. Lead isn't listed in the metals above. Furthermore, as you'll see in the list below, the ATF has specifically stated that the SS109/M855 bullets are exempted from AP status.
ATF AP Classified Rounds
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 (not copper)
OMNISHOCK .38 Special with steel core
7.62×39 ammo with steel core bullets
ATF Exempted Rounds
5.56 SS109 and M855 NATO rounds, with steel penetrator tip.
.30-06 M2 AP ammo
Source Military Ammunition and Why Green Tip M855 is Not Armor Piercing : ITS Tactical
(17)(A) The term "ammunition" means ammunition or cartridge cases, primers, bullets, or propellent powder designed for use in any firearm.
(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.
(C) The term "armor piercing ammunition" does not include shotgun shot required by Federal or State environmental or game regulations for hunting purposes, a frangible projectile designed for target shooting, a projectile which the Attorney General finds is primarily intended to be used for sporting purposes, or any other projectile or projectile core which the Attorney General finds is intended to be used for industrial purposes, including a charge used in an oil and gas well perforating device.
What does all that mean?
A few things to take note of is that the classification as "armor piercing" is for bullets only, not the complete cartridge. Despite the mention of handgun caliber above, you can take that to mean that it's a round that has been made as a handgun caliber at some point.
The bullet (projectile) must also have a core made entirely out of the metals listed above, or be a full jacketed bullet with a jacket weighing more than 25% of its overall weight. This means that the SS109/M855 bullets wouldn't be covered, as their cores are partly steel, and partly lead. Lead isn't listed in the metals above. Furthermore, as you'll see in the list below, the ATF has specifically stated that the SS109/M855 bullets are exempted from AP status.
ATF AP Classified Rounds
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 (not copper)
OMNISHOCK .38 Special with steel core
7.62×39 ammo with steel core bullets
ATF Exempted Rounds
5.56 SS109 and M855 NATO rounds, with steel penetrator tip.
.30-06 M2 AP ammo
Source Military Ammunition and Why Green Tip M855 is Not Armor Piercing : ITS Tactical
