Any 5 parts can be US made parts as there in no percentage but the acutal number of imported parts allowed(10).
The list of parts of a imported rifle is
(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) Forearm handguards
(18) Magazine bodies
(19) Followers
(20) Floorplates
A stamped reciever AK rifle doesn't have parts 3,5,8,10,or 14. So it only has 15 of the 20 listed parts.
A milled receiver AK rifle doesn't have parts 3,4,5,8,10,or 14. So it only has 14 of the 20 listed parts.
If a muzzle nut is welded on the barrel it is not considered a muzzle device.