just watch out for any " constructive possession" issues.
There are kits out there, IIRC "80% Kits" that you can buy and do the finish work on to make them into a completed weapon.
I know that is the case for 1911's and AK-47's. The AK kits are pretty much a flat stamped piece of sheet metal that need some finishing work like holes drilled, then you slap it into a bending jig, perform a few operations, and you have a AK lower ready to finish.
There are all sorts of people out there with "mini mills" or old surplus machines that are banging out 1911 frames for personal use. Once you start selling them in any quantity, you will run afoul of the Feds, but you can serialize any you make for personal use and sell them legally so long as they are properly marked.
Personally I'd love to build a 1911 that way