I heard something today, that made me go .

Someone I know casually, who knows I'm into AR's told me about someone they know "honestly", who is building what sounds like an 80% lower. What I was told, is that they can't find anyone to anodize it, because adding the finish changes the dimensions of the receiver, and runs afoul of ATF regs.

I flat out laughed when I heard this, but they insisted this was the case.

I realize there are some weird rules, so I figured I'd ask.

It runs afoul of ATF because it is now a gun. Who ever does the work (Anodizing) is working on a firearm.
Both you and the place doing the andozing need to use caution. Both with shipping and a non-FFL working on a firearm.

If you ship it off to one of the well known anodizing places that has an FFL they will want to see a serial # and they would log it into their books.

Possibly destroying the unknown factor you may have been trying to maintain by machining your own.

You might be legal if you take it to a local anodizer and you stay there and maintain possession while they work on it, but then what do I know.

Of course you can send it anywhere to be anodized before you do any machine work on it but then you need to be careful about scratches when finishing.

Honestly, this isn't mine!

I suspected it had to do with the serial number, but this guy swore is was the added thickness of the coating.

FWIW, I just by stripped receives to add to the hoard. I'm already on all the pertinent lists, so one more or less isn't going to matter much. It just sounded bogus to me.