The ATF.GOV links are very clear for the requirements of both importers and domestic manufactures. What is lease clear is what can be removed. They are very clear about the serial number and no so much about the other.
The Gun Control Act of 1968 at Title 18 United States Code (U.S.C.) 923(i) provides, in
part,
that licensed manufacturers and licensed importers must identify each firearm
manufactured or imported by a serial number in the manner prescribed by regulation. The
NFA at 26 U.S.C. 5842 provides, in relevant part, that manufacturers, importers, and
anyone making a firearm shall identify each firearm manufactured, imported, or made by a
serial number, the name of the manufacturer, importer, or maker, and such other
identification prescribed by regulation. Title 27 Code of Federal Regulations (CFR)
478.92(a)(1) and 479.102(a) further require the licensed manufacturer, licensed importer,
or maker of a firearm to legibly identify each firearm manufactured, imported, or made by
engraving, casting, stamping (impressing), or otherwise conspicuously placing the
individual serial number on the frame or receiver, and certain additional information - the
model (if designated), caliber/gauge, manufacturer/importer’s name, and place of origin -
on the frame, receiver, or barrel. Both regulations require the serial number to be at a
minimum depth and print size, and the additional information to be at a minimum depth.
Further, the serial number must be placed in a manner not susceptible of being readily
obliterated, altered, or removed, and not duplicate any serial number placed by the licensed
manufacturer, licensed importer, or maker on any other firearm. Under 18 U.S.C. 922(k)
and 26 U.S.C. 5861(g), i
t is unlawful for any person to possess or receive any firearm
which has had the serial number removed, obliterated, or altered
some more here
https://www.federalregister.gov/docu...earms-98r-341p
https://fflconsultinggroup.com/licen...ture-firearms/
Federal gun manufacturing laws apply to persons engaged in the assembly of guns for profit and livelihood (ATF Rul.2010-10;Revenue Ruling 55-342) . Some FFLs mistakenly believe that gun assembly and disassembly, or simply building guns from distinctive parts is not considered “manufacturing” and therefore doesn’t require a Type 07 Federal Firearms License. FFLs may consider this type of activity to be gunsmithing. ATF licensees should be careful and secure the proper federal firearms license for the type of activity they engage in.