What determines the serialed part?

[CleverNickname]

Ok, we all know guns manufactured for sale in the US have to have a serial number on the receiver. But what rule determines what the receiver is? I was under the impression that for a semi-auto gun the determining factor was the receiver was the part that held the magazine. For example, the ARs I have follow this rule, as the lower receiver is marked. My FAL follows this, as the upper receiver is marked. However, I got an FNC last week, and while the lower receiver is the part that has the magazine well (just like an AR), the lower has no serial number. Only the upper does. Is there a hard-and-fast rule that says where the serial number must go, or does the manufacturer just choose?

 

[CZ-75]

I'd gather that it is the BATF that chooses.

For rifles and shotguns, the definition, and thereby the part to be regulated, should be the portion that RECEIVES the barrel. If the barrel doesn't attach to it, it ought not to be considered the "receiver." Makes too much sense, I'm sure, for bureaucrats.

 

[Hkmp5sd]

It depends....

(a)(1) Firearms. Each licensed manufacturer or licensed importer of any firearm manufactured or imported shall legibly identify each such firearm by engraving, casting, stamping (impressing), or otherwise conspicuously placing or causing to be engraved, cast, stamped (impressed) or placed on the frame or receiver thereof in a manner not susceptible of being readily obliterated, altered, or removed, an individual serial number not duplicating any serial number placed by the manufacturer or importer on any other firearm, and by engraving, casting, stamping (impressing), or otherwise conspicuously placing or causing to be engraved, cast, stamped (impressed) or placed on the frame, receiver, or barrel thereof in a manner not susceptible of being readily obliterated, altered or removed, the model, if such designation has been made; the caliber or gauge; the name (or recognized abbreviation of same) of the manufacturer and also, when applicable, of the importer; in the case of a domestically made firearm, the city and State (or recognized abbreviation thereof) wherein the licensed manufacturer maintains its place of business; and in the case of an imported firearm, the name of the country in which manufactured and the city and State (or recognized abbreviation thereof) of the importer.

Firearm frame or receiver. That part of a firearm which provides housing for the hammer, bolt or breechblock, and firing mechanism, and which is usually threaded at its forward portion to receive the barrel.

http://www.atf.treas.gov/pub/fire-explo_pub/complete.htm