OK look I am gonna do this one more time and then I'm done.
It's in English. It is not my fault that you cannot or will not understand it.
Please follow along carefully.
1) 27 C.F.R. § 479.102 states in part:
(a) You, as a manufacturer, importer, or maker of a firearm, must legibly identify the firearm as follows:
Please note that they say BOTH maker and manufacturer here. This is the section of LAW that requires a gun maker/manufacturer (please note they use both again) to mark firearms in certain ways.
2)National Firearms Act, enacted by Congress, defines the term MAKE to mean:
Make. The term "make", and the various derivatives of such word,
shall include manufacturing (other than by one qualified to engage in
such business under the NFA), putting together, altering, any
combination of these, or otherwise producing a firearm.
So far we have 2 things, a law that says MAKERS must engrave firearms in a certain manner and a law that defines MAKE to mean more than just the original manufacture, it means to produce a firearm by modification as well, the purpose of the 5320.1
3) Regular firearms manufacturers don't use the 5320.1, it says:
Federal firearms license to manufacture firearms (Type 07 or 10) and who has paid special (occupational) tax to manufacture NFA firearms
is exempt from the making tax and filing of the ATF Form 1
application. Such qualified manufacturer must report and register each
NFA firearm manufactured by filing ATF Form 2.
So we see that a Form 1 is for you and I, not regular firearm makers.
And section h of the Form 1 says:
Serial Numbers and other Markings. If an existing firearm is being
modified into an NFA firearm, enter the existing serial number of the
firearm into item 4g and the name and address of the original
manufacturer into item 4a. Do not Alter or Modify the existing
Serial Number. If the NFA firearm is being made from parts, your
name and address are to be entered into 4a and a serial number you
create is to be entered into item 4g.
Again we see this term MAKE. Hmm, we are MAKING a firearm with a 5320.1? We are?
And why does it say ORIGINAL MANUFACTURER? Well that's because there is a NEW maker now, the person named on the Form 1.
Well then if we are the MAKER, then 27 C.F.R. § 479.102 would apply to us since we've already seen that it requires:
You, as a manufacturer, importer, or maker of a firearm
Wait, you mean we MADE something with a Form 1, and that's different than MANUFACTURING it? So since we are the MAKER then we must follow the law.
Please note that 27 CFR 479.102 has nothing to do with the National Firearms Act, which is why the NFA branch doesn't give a crap whether you engrave the thing or not.
You are still in violation of 27 CFR 479.102, not the National Firearms Act, if you fail to mark a firearm you MADE in a certain manner.
The Supreme Court has held, as has just about every other court ever seated, that not knowing the law is not a justification for breaking it.
The courts have also held repeatedly that it is NOT the responsibility of governments to inform you of every law, that is YOUR responsibility.
So, just because some ATF agent doesn't know what they are doing does not relieve you of your responsibility to follow the law.
So that is how the boatload of lawyers that have looked at this come to the conclusion that if you MAKE a firearm then you must MARK it as the MAKER.
It's English, it's law, and you can do with it what you will.
27CFR 479.102 goes on to tell us what must be marked:
(i) The model, if such designation has been made;
(ii) The caliber or gauge;
(iii) Your name (or recognized abbreviation) and also, when applicable, the name of the foreign manufacturer or maker;
(iv) In the case of a domestically made firearm, the city and State (or recognized abbreviation thereof) where you as the manufacturer maintain your place of business, or where you, as the maker, made the firearm; and
Well since the 5320.1 told us to re-use the serial number, and since the caliber or gauge is already there, what is missing?
The name, city, state where the firearm was MADE which is what every person that has an actual CLUE has done with every firearm they have made with a Form 1 at least as early as the late 1970's (that's the oldest gun made on a Form 1 I've seen).
So it's not new at all, there has been no change or reversal of the law, merely the ATFs understanding of it, which given their track record is to be expected.
That does not, again, relieve you of your responsibility to follow the law, the printed, Congressional approved, codified, stained in blood and concrete statute.
There is no wiggle room here, it's very clear.