Which is why the US parts issue is not enforceable.
If you have access to a machine shop that could produce identical parts to the imported ones, there is no way to detemine what was made where. Materials of construction cannot be used as there is no restriction on using imported metals. Cast parts might be a problem as I don't know of many available machine shops that have casting facilities. Everything else is fair game.
Anyone here have a woodshop in their garage? That makes prosecution on the wood parts impossible.
Oh, there is no requirement for a part made in the US to be marked as such. Here's the neat part of this . If a imported part was modified to where it no longer useable for it's original function and then returned to useable condition; it is now a US part. For example, a cut receiver that is reconstructed is a US part. So, if a imported part that is marked as such is reconstructed; it is now a US part that has imported markings.
The first case the BATF prosecutes on 922r will get thrown out of court which is more than likely the reason there has not been any cases brought on 922r.