Lets go with, like I said above, the ATF, and not wikipedia.
http://www.atf.treas.gov/pub/fire-ex...b/complete.htm
Semiautomatic
assault weapon.
(a) Any of the firearms, or copies or duplicates of the firearms in any caliber, known as:
(1) Norinco, Mitchell, and Poly Technologies Avtomat Kalashnikovs (all models),
(2) Action Arms Israeli Military Industries UZI and Galil,
(3) Beretta Ar70 (SC-70),
(4)
Colt AR-15,
(5) Fabrique National FN/FAL, FN/LAR, and FNC,
(6) SWD M-10, M-11, M-11/9, and M-12,
(7) Steyr AUG,
(8) INTRATEC TEC-9, TEC-DC9 and TEC-22, and
(9) 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 --
(1) A folding or telescoping stock,
(2) A pistol grip that protrudes conspicuously beneath the action of the weapon,
(3) A bayonet mount,
(4) A flash suppressor or threaded barrel designed to accommodate a flash suppressor, and
(5) A grenade launcher;