This is from a thread I did on FAL compliance, but the info is still the same:
922r and what it means to the DIYer
US Code 18 Section 922 "Unlawfull Acts", paragraph (r) affects the building of an imported assault weapon....
"(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"
925(d)(3) states
"is of a type that does not fall within the definition of a
firearm as defined in section 5845(a) of the Internal Revenue
Code of 1986 and is generally recognized as particularly suitable
for or readily adaptable to sporting purposes, excluding surplus
military firearms, except in any case where the Attorney General
has not authorized the importation of the firearm pursuant to
this paragraph, it shall be unlawful to import any frame,
receiver, or barrel of such firearm which would be prohibited if
assembled; or"
Now we get to the definition of the assault weapon and the 20 forbidden parts. The way it works is if the weapon is composed of 10 or less of these parts that are foreign made then the weapon in question is not foreign made. In other words if you have 11 or more of these on the weapon it is foreign made and you have broken the law. The following is referred to as the 1989 Import Ban.
"
18 USC Chapter 44 as amended by Public Law 101-647 (enacted 11-29-90) and 27 CFR part 178 as amended 06-25-93.
§ 178.39 Assembly of semiautomatic rifles or shotguns.
(a) No person shall assemble a semiautomatic rifle or any shotgun using more than 10 of the imported parts listed in paragraph (c) of this section if the assembled firearm is prohibited from importation under section 925(d)(3) as not being particularly suitable for or readily adaptable to sporting purposes.
925(d)(3) includes FN FAL (L1A1) style semiautomatic rifle with folding stock, military style stock with separate pistol grip, threaded muzzle, flash hider, grenade launcher, bayonet lug, or night sights. Note: FN FAL (L1A1) style semiautomatic rifles having a thumbhole style stock without the above features were approved for importation from 1989 to 1994. In 1994 BATFE changed their interpretation to eliminate the exemption for firearms with thumbhole stocks.
(c) For purposes of this section, the term "imported parts" are:"
1. Frame-Receiver
2. Barrel
3. Barrel Extension
4. Mounting Block/Trunnion
5. Muzzle Attchment
6. Bolt
7. Bolt Carrier
8. Operating Rod (charging handle)
9. Gas Piston
10. Trigger Housing
11. Trigger
12. Hammer
13. Sear
14. Disconnector
15. Buttstock
16. Pistol Grip
17. Forearm/Handguard
18. Magazine Body
19. Magazine Follower
20. Magazine Floor Plate