From the internet:
ATF Special Advisory issued April 7, 2014
TEST, EXAMINATION AND CLASSIFICATION OF 7N6 5.45X39 AMMUNITION
On March 5, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) received a request from the U.S. Customs and Border Protection agency (CBP) to conduct a test, examination and classification of Russian-made 7N6 5.45x39 ammunition for purposes of determining whether it is considered “armor piercing ammunition” as defined by the Gun Control Act (GCA), as amended. Since 1986, the GCA has prohibited the importation of armor piercing ammunition unless it is destined for government use or testing. The imported ammunition about which CBP was inquiring was not destined for either excepted purpose.
The Gun Control Act of 1968 (GCA), as amended, defines the term “armor piercing ammunition” as:
“(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.” (emphasis added)
When ATF tested the 7N6 samples provided by CBP, they were found to contain a steel core. ATF’s analysis also concluded that the ammunition could be used in a commercially available handgun, the Fabryka Bronie Radom, Model Onyks 89S, 5.45x39 caliber semi-automatic pistol, which was approved for importation into the United States in November 2011. Accordingly, the ammunition is “armor piercing” under the section 921(a)(17)(B)(i) and is therefore not importable. ATF’s determination applies only to the Russian-made 7N6 ammunition analyzed, not to all 5.45x39 ammunition. Ammunition of that caliber using projectiles without a steel core would have to be independently examined to determine their importability