The barrel counts only as much as the other 19 parts when considering US or foreign manufacture. You only count the parts on a particular gun and keep the foreign parts under 11. Swap furniture, magazine components and a flash hider for US parts and many guns can technically be imported.
The other way to get legal is to to weld on a muzzle brake, remove bayonet lug and folding stocks making it a 'sporting' configuration. This is how they import a lot of AKs then swap in enough US parts and put the fun bits back on.
*****
The US Law that prohibits import of 'non-Sporting' firearms...
Title 18 Chapter 44 Section 922(r)
(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.
***
Explanation of which Imported parts add up to the limit of 10 before a post ban firearm is no longer legal in the US....
TITLE 27--ALCOHOL, TOBACCO PRODUCTS AND FIREARMS
CHAPTER II--BUREAU OF ALCOHOL, TOBACCO, FIREARMS, AND EXPLOSIVES,
DEPARTMENT OF JUSTICE
PART 478--COMMERCE IN FIREARMS AND AMMUNITION--Table of Contents
Subpart C--Administrative and Miscellaneous Provisions
Sec. 478.39 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. 478.151; 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
[T.D. ATF-346, 58 FR 40589, July 29, 1993]
***
In addition to 922(r), you generally (without NFA or other licencing) can't have the following in the US:
- A barrel on a rifle less than 16" (no 14.5" M4)
- Any receiver that readily convertible to fully auto (e.g. FAL with auto sear cut is considered a machine gun)
- Any Receiver that was once a fully automaic (Once a machine gun always a machine gun e.g. no converted auto classification)
- Or an open bolt gun (No Sterling Police Carbine)
- Newly imported Norinco products
