Once the insults begin, it's time for me to bow out. You didn't like my answer - neither did I. Most of us would like a never ending supply of new transferrable MGs but that isn't reality. "Replacement" MGs need to be registered. If you want to pretend you are Hatton Industries and it's 1985 while you are building a paperless 240 today or are confident in your ability to convince a jury a sliver of metal with a removed serial # is a machinegun while the 24 pound piece of metal next to it that looks and acts like a machinegun is just cosmetics and you are not really building anything, knock yourself out - risk vs reward. For those interested, here is the statute and referenced regulation in its entirety. Each reader can decide if I am "twisting" anything. I'm too lazy to copy the statutes about removing serial numbers. 18 USC 922(k) and 26 USC 5861(g)
§5841. Registration of firearms
(a) Central registry
The Secretary shall maintain a central registry of all firearms in the United States which are not in the possession or under the control of the United States. This registry shall be known as the National Firearms Registration and Transfer Record. The registry shall include—
(1) identification of the firearm;
(2) date of registration; and
(3) identification and address of person entitled to possession of the firearm.
(b) By whom registered
Each manufacturer, importer, and maker shall register each firearm he manufactures, imports, or makes. Each firearm transferred shall be registered to the transferee by the transferor.
(c) How registered
Each manufacturer shall notify the Secretary of the manufacture of a firearm in such manner as may by regulations be prescribed and such notification shall effect the registration of the firearm required by this section. Each importer, maker, and transferor of a firearm shall, prior to importing, making, or transferring a firearm, obtain authorization in such manner as required by this chapter or regulations issued thereunder to import, make, or transfer the firearm, and such authorization shall effect the registration of the firearm required by this section.
(d) Firearms registered on effective date of this Act
A person shown as possessing a firearm by the records maintained by the Secretary pursuant to the National Firearms Act in force on the day immediately prior to the effective date of the National Firearms Act of 1968 1 shall be considered to have registered under this section the firearms in his possession which are disclosed by that record as being in his possession.
(e) Proof of registration
A person possessing a firearm registered as required by this section shall retain proof of registration which shall be made available to the Secretary upon request.
§ 479.103 Registration of firearms manufactured.
Each manufacturer qualified under this part shall file with the Director an accurate notice on Form 2 (Firearms), Notice of Firearms Manufactured or Imported, executed under the penalties of perjury, to show his manufacture of firearms. The notice shall set forth the name and address of the manufacturer, identify his special (occupational) tax stamp and Federal firearms license, and show the date of manufacture, the type, model, length of barrel, overall length, caliber, gauge or size, serial numbers, and other marks of identification of the firearms he manufactures, and the place where the manufactured firearms will be kept. All firearms manufactured by him during a single day shall be included on one notice, Form 2 (Firearms), filed by the manufacturer no later than the close of the next business day. The manufacturer shall prepare the notice, Form 2 (Firearms), in duplicate, file the original notice as prescribed herein and keep the copy with the records required by subpart I of this part at the premises covered by his special (occupational) tax stamp. Receipt of the notice, Form 2 (Firearms), by the Director shall effectuate the registration of the firearms listed on that notice. The requirements of this part relating to the transfer of a firearm are applicable to transfers by qualified manufacturers.