How many US parts required to build rifle?

18 USC 922r states that it is illegal to assemble from imported parts any rifle or shotgun which would be illegal to import - i.e., anything not considered a "sporting" weapon. Title 27 Chapter 1 Section 178.39 states..

"(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."

Thus, the rifle you assemble, if it is banned from importation without the compliance parts, cannot contain more than 10 of the following "countable" parts, and the number of US made compliance parts necessary will be based on how many parts there are to the weapon according to the BATFE breakdown chart.

"Countable" parts include:

(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 *