It comes down to an exectutive order, 922r:
(The saigas are considered sporting, I believe, and that--again, I *think* makes them exempt. Not sure about the SKS. And yeah, that order/ruling/law is complete BS and an outright attack on the Consititution.)
Legalese, for what it's worth:
http://www.atf.treas.gov/regulations/27cfr178.html
922 (r)
The Imported Parts Law(1990)
178.39 otherwise known as 922(r) 10 Foreign parts law on semiauto Rifles & Shotguns
http://www.atf.treas.gov/regulations/27cfr178.html
Sec. 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.
(b) The provisions of this section shall not apply to:
(1) The assembly of 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 such rifle or shotgun for the purposes of
testing or experimentation authorized by the Director under the
provisions of Sec. 178.151; or
(3) The repair of any rifle or shotgun which had been imported into or assembled in the United States prior to November 30, 1990, or the replacement of any part of such firearm.
(c) For purposes of this section, the term imported parts are:
(1) Frames, receivers, receiver castings, forgings or stampings
(2) Barrels
(3) Barrel extensions
(4) Mounting blocks (trunions)
(5) Muzzle attachments
(6) Bolts
(7) Bolt carriers
(8) Operating rods
(9) Gas pistons
(10) Trigger housings
(11) Triggers
(12) Hammers
(13) Sears
(14) Disconnectors
(15) Buttstocks
(16) Pistol grips
(17) Forearms, handguards
(18) Magazine bodies
(19) Followers
(20) Floorplates
*****THE "ASSault weapon ban is dead. 922v no longer applies*****
922 (v)
The Assault Weapon Ban(1994)
(v)(1) It shall be unlawful for a person to manufacture, transfer,
or possess a semiautomatic assault weapon.
(2) Paragraph (1) shall not apply to the possession or transfer of any semiautomatic assault weapon otherwise lawfully possessed under Federal law on the date of the enactment of this subsection.
(3) Paragraph (1) shall not apply to--
(A) any of the firearms, or replicas or duplicates of the
firearms, specified in Appendix A to this section, as such firearms were manufactured on October 1, 1993;
(B) any firearm that--
(i) is manually operated by bolt, pump, lever, or slide
action;
(ii) has been rendered permanently inoperable; or
(iii) is an antique firearm;
(C) any semiautomatic rifle that cannot accept a detachable
magazine that holds more than 5 rounds of ammunition; or
(D) any semiautomatic shotgun that cannot hold more than 5 rounds of ammunition in a fixed or detachable magazine.
The fact that a firearm is not listed in Appendix A shall not be
construed to mean that paragraph (1) applies to such firearm. No firearm exempted by this subsection may be deleted from Appendix A so long as this subsection is in effect.
(4) Paragraph (1) shall not apply to--
(A) the manufacture for, transfer to, or possession by the
United States or a department or agency of the United States or a State or a department, agency, or political subdivision of a State,or a transfer to or possession by a law enforcement officer employed by such an entity for purposes of law enforcement (whether on or off duty);
(B) the transfer to a licensee under title I of the Atomic
Energy Act of 1954 for purposes of establishing and maintaining an on-site physical protection system and security organization required by Federal law, or possession by an employee or contractor
of such licensee on-site for such purposes or off-site for purposes of licensee-authorized training or transportation of nuclear materials;
(C) the possession, by an individual who is retired from service with a law enforcement agency and is not otherwise prohibited from receiving a firearm, of a semiautomatic assault weapon transferred to the individual by the agency upon such retirement; or
(D) the manufacture, transfer, or possession of a semiautomatic assault weapon by a licensed manufacturer or licensed importer for the purposes of testing or experimentation authorized by the Secretary.
921(a) (30) Definition of semiauto assault weapons
(30) The term ``semiautomatic assault weapon'' means--
(A) any of the firearms, or copies or duplicates of the firearms in any caliber, known as--
(i) Norinco, Mitchell, and Poly Technologies Avtomat
Kalashnikovs (all models);
(ii) Action Arms Israeli Military Industries UZI and Galil;
(iii) Beretta Ar70 (SC-70);
(iv) Colt AR-15;
(v) Fabrique National FN/FAL, FN/LAR, and FNC;
(vi) SWD M-10, M-11, M-11/9, and M-12;
(vii) Steyr AUG;
(viii) INTRATEC TEC-9, TEC-DC9 and TEC-22; and
(ix) revolving cylinder shotguns, such as (or similar to)
the Street Sweeper and Striker 12;
(B) a semiautomatic rifle that has an ability to accept a
detachable magazine and has at least 2 of--
(i) a folding or telescoping stock;
(ii) a pistol grip that protrudes conspicuously beneath the
action of the weapon;
(iii) a bayonet mount;
(iv) a flash suppressor or threaded barrel designed to
accommodate a flash suppressor; and
(v) a grenade launcher;
(C) a semiautomatic pistol that has an ability to accept a
detachable magazine and has at least 2 of--
(i) an ammunition magazine that attaches to the pistol
outside of the pistol grip;
(ii) a threaded barrel capable of accepting a barrel
extender, flash suppressor, forward handgrip, or silencer;
(iii) a shroud that is attached to, or partially or
completely encircles, the barrel and that permits the shooter to hold the firearm with the nontrigger hand without being burned;
(iv) a manufactured weight of 50 ounces or more when the pistol is unloaded; and
(v) a semiautomatic version of an automatic firearm; and
(D) a semiautomatic shotgun that has at least 2 of--
(i) a folding or telescoping stock;
(ii) a pistol grip that protrudes conspicuously beneath the
action of the weapon;
(iii) a fixed magazine capacity in excess of 5 rounds; and
(iv) an ability to accept a detachable magazine.
