The MN statute is:
609.667 FIREARMS; REMOVAL OR ALTERATION OF SERIAL NUMBER.Whoever commits any of the following acts may be sentenced to imprisonment for not more than five years or to payment of a fine of not more than $10,000, or both:
(1) obliterates, removes, changes, or alters the serial number or other identification of a firearm;
(2) receives or possesses a firearm, the serial number or other identification of which has been obliterated, removed, changed, or altered; or
(3) receives or possesses a firearm that is not identified by a serial number.
As used in this section, "serial number or other identification" means the serial number and other information required under United States Code, title 26, section 5842, for the identification of firearms.
The US Code referenced is:
26 U.S.C. § 5842 - U.S. Code. Identification of firearms(a) Identification of firearms other than destructive devices.--Each manufacturer and importer and anyone making a firearm shall identify each firearm, other than a destructive device, manufactured, imported, or made by a serial number which may not be readily removed, obliterated, or altered, the name of the manufacturer, importer, or maker, and such other identification as the Secretary may by regulations prescribe.
(b) Firearms without serial number.--Any person who possesses a firearm, other than a destructive device, which does not bear the serial number and other information required by subsection (a) of this section shall identify the firearm with a serial number assigned by the Secretary and any other information the Secretary may by regulations prescribe.
(c) Identification of destructive device.--Any firearm classified as a destructive device shall be identified in such manner as the Secretary may by regulations prescribe.
But here's the thing. 26USC5842 is part of the National Firearms Act, and in it we find definitions:
26 U.S.C. § 5845. DefinitionsFor the purpose of this chapter--
(a) Firearm.--The term “firearm” means (1) a shotgun having a barrel or barrels of less than 18 inches in length; (2) a weapon made from a shotgun if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 18 inches in length; (3) a rifle having a barrel or barrels of less than 16 inches in length; (4) a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length; (5) any other weapon, as defined in subsection (e); (6) a machinegun; (7) any silencer (as defined in section 921 of Title 18, United States Code); and (8) a destructive device. The term “firearm” shall not include an antique firearm or any device (other than a machinegun or destructive device) which, although designed as a weapon, the Secretary finds by reason of the date of its manufacture, value, design, and other characteristics is primarily a collector's item and is not likely to be used as a weapon.
In other words, the serial number requirements in the section referenced by MN Stat 609.667 applies only to NFA firearms. This kind of thing is
exactly why I don't put too much weight on my own legal research.
It's certainly possible that a MN court will interpret that the reference to federal law is only for the purpose of describing how markings must be done, and not for the purpose of defining which firearms must be marked. But at best this is an ambiguous law, and I'd argue that the case should be dismissed as being unconstitutionally vague.
