/yeah, 922r has some weird history behind it--it is one of the few gun laws dealing with importation that actually DIDN'T start out as some sort of international gun-grabbing ploy by the UN. It started out as part of a "trade agreement", and it has to do with setting standards for US manufacturers who were importing surplus foreign arms and "remanufacturing" them for sale in the US as "US-Made"...
To be branded as "US Made", a thing (TV, automobile, firearm, etc) has to have, at the minimum, 30% of the parts in it, manufactured here in the US. "Made" is a fairly loosely-defined word in this case, and some industries (like the auto industry) get HUGE amounts of leeway with regards to parts being "made" in the US.
But although 922r started life as a "trade bill" it soon became embroiled in the anti-gun debate, and got turned into a way to try and control the sale of "de-militarized" firearms from other countries being iimported, converted, and sold to collectors and enthusiasts. As it stands now, 922r is really nothing more than a series of difficult hoops for importers and manufacturers to jump through so that they can sell surplus firearms to US citizens, and a set of egregious restrictions on law-abiding citizens that the BATFE uses to harass innocent people who most of the time don't even know this sill set of laws exists...
So with 922r, the exact number of parts in a gun that have to be US-made isn't a set number it is dependent on the TOTAL number of parts n the gun, and then it's got to be 30% of that, and the parts that are replaced must be "functional parts" of the gun's "original configuration and design". So while things like scope mounts, cheek rests, bipods, and optics don't count toward 922r compliance (which IMO is utter BS) parts that are just as easily swapped out and may or not be integral to the mechanical functioning of the gun (forearm grips, buttstocks, etc) definitely DO count, because they were degisned on the gun in it's stock form...
The entire 922r requirements system s utter BS as applied to private ownership, and needs to be amended to exempt private owners from compliance. If I want to replace the crappy hard hollow plastic furniture on my Century Arms rifle with original H&K factory furniture (which is WAY more comfortable, durable, and better looking) then once I've got the gun in y ownership, I should be able to swap whatever parts I want on it.
What is MOSt frustrating is that there are a LOT of parts on these guns that ARE functional that don't count, or simply aren't available as US manufacture--trigger group pins and springs, screws and pins in the furniture, etc...
It's a silly law and should be changed so that it ONLY applies to the original "manufacturer" of the firearm.
If I want to take my old Chevy and restore it, and I replace 90% of the parts on it with parts from Brazil, China, and Singapore, THAT is totally legal. As long as I'm not a dealer, trying to sell it as an original, US-made car, it's private property, and I can do anything with it I want, as long as it will pass state safety inspections.
The same should go with these "remanufactured" firearms. Once they are sold by the dealer, then there is NO logical, moral, or legal reason why the private owner shouldn't be allowed to do whatever they want with it with regards to parts, as long as they don't do anything that breaks other established laws (like put in a full-auto TCG, or make it an SBR, or whatever)...