I am not a lawyer, none of this may be taken as legal advice.
Always verify this information with your a written letter to the ATF, they are very responsive. The ATF has been know to change their mind regularly then change it back.
922r is the section of law which relates to assembling or modifying semi-automatic weapons, such as AK and SKS type rifles. This is my understanding of the law after reading the law and several people's descriptions of it. I am not a lawyer, so take this interpretation as such; if you want the actual definition, please consult a lawyer.
922r is defined under U.S. Code - Title 18 - Part 1 - Chapter 44 - § 922
(r) It shall be unlawful for any person to assemble from imported parts any semiautomatic rifle or any shotgun which is identical to any rifle or shotgun prohibited from importation under section 925 (d)(3) of this chapter as not being particularly suitable for or readily adaptable to sporting purposes except that this subsection shall not apply to —
(1) the assembly of any such rifle or shotgun for sale or distribution by a licensed manufacturer to the United States or any department or agency thereof or to any State or any department, agency, or political subdivision thereof; or
(2) the assembly of any such rifle or shotgun for the purposes of testing or experimentation authorized by the Attorney General.
So, what does that mean? Simply: You may only use 10-or-fewer foreign made parts.
This work is heavily based on Dinzag's Parts Count article. It is loosely based on another 922r Worksheet, which seems to have disappeared.
This project is hosted on my github repository, you may clone the project or contact me there.
If you find any mistakes, which I am prone to making, please let me know.