Interestingly there is this part in the new bill (attention to highlighted part):
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IANAL, but hasn't the GCA68 been interpreted that ONLY licensed dealers need serial numbers?
From Wikepedia:
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It would seem that if you are making any firearm - outside of one that is 3D printed - even if it is unserialized and for your use, you should be okay
ETA - similar thoughts just ahead of me typing this
Good catch.