More to the story (can't edit the somewhat misleading thread title):
https://www.ammoland.com/2020/12/atf...#axzz6gRyl2n3A
Apparently, it's Polymer 80's "buy, build, shoot" kits that are the problem, b/c while they are still 80% at time of sale, everything needed to assemble a working firearm (after machining is complete) is included.
https://www.ammoland.com/2020/12/mot...#axzz6gRyl2n3A