There are going to be parallel issues this summer when the ATF puts new '80%' rules into effect (and states, e.g. WA, are doing similar things), Some of the proposed definitions of when something becomes a firearm are pretty far up stream, even as far as anything has been done that makes it not just a commodity item.
So, is a raw forging a 'firearm'? Step 1 of the process has certainly been done. But what about these:
https://www.80percentarms.com/produc...ower-receiver/
4.5x1.5 might be a stock size, but when you cut it to 8 inches *for the purpose of making an AR lower*, is that step 1 as well? Is the only safe way to buy a stock size, say 5x1.5x12 and cut it down?