This is an ellaboration on my comment in The Filthy Lying NRA and Their Incredibly Slick Phone Operators
The UN Small Arms treaty sounds as if it would influence US firearms laws the same way that the Schengen Treaty influenced the Swiss firearms laws. The Schengen Agreements have created a borderless Schengen Area, which operates very much like a single state for international travel with border controls for travellers travelling in and out of the area, but with no internal border controls. Part of these changes was to harmonise laws in order to eliminate customs checks. One major change in the Swiss Firearms law is that Gun trade among individuals will require a valid weapon acquisition permit which is a radical restriction, from a Swiss point of view, that is assumed will undercut private gun trade dramatically.
The aim of a potential U.N. arms treaty is to combat the illicit international trade of small arms by "tightening regulation of, and setting international standards for, the import, export and transfer of conventional weapons" in order to "close gaps in existing regional and national arms export control systems that allow weapons to pass onto the illicit market." Even if such a treaty came to pass, U.S. rights and laws regarding the sale and ownership of small arms would still apply within the United States.
The problem is that the Supreme Court said that laws imposing conditions and qualifications on the commercial sale of arms were acceptable in Heller-McDonald. Additionally, Registration was acceptable as well. The only issue is whether the US would implement those Constitutionally acceptable restrictions.
I do like how the Snopes piece on this ended:
There is no "legal way around the 2nd Amendment" other than a further amendment to the Constitution that repeals or alters it, or a Supreme Court decision that radically reinterprets how the 2nd Amendment is to be applied.
I thought that already happened with Heller-McDonald.