Every challenge was put down by the Court:
A February 2013 Congressional Research Service (CRS) report to Congress said that the "Assault Weapons Ban of 1994 was unsuccessfully challenged as violating several constitutional provisions." The report said that challenges to three constitutional provisions were easily dismissed. The ban did not make up an impermissible Bill of Attainder.[19]:31 It was not unconstitutionally vague.[20] And it was not incompatible with the Ninth Amendment.
Challenges to two other provisions took more time to decide.
In evaluating challenges to the ban under the Commerce Clause, the court first evaluated Congress' authority to regulate under the clause, and second analyzed the ban's prohibitions on manufacture, transfer, and possession. The court held that "it is not even arguable that the manufacture and transfer of 'semiautomatic assault weapons' for a national market cannot be regulated as activity substantially affecting interstate commerce." It also held that the "purpose of the ban on possession has an 'evident commercial nexus.'"
The law was also challenged under the Equal Protection Clause. It was argued that it banned some semi-automatic weapons that were functional equivalents of exempted semi-automatic weapons and that to do so based upon a mix of other characteristics served no legitimate governmental interest. The reviewing court held that it was "entirely rational for Congress ... to choose to ban those weapons commonly used for criminal purposes and to exempt those weapons commonly used for recreational purposes." It also found that each characteristic served to make the weapon "potentially more dangerous," and were not "commonly used on weapons designed solely for hunting."
The federal assault weapons ban was never directly challenged under the Second Amendment.
https://en.wikipedia.org/wiki/Federal_Assault_Weapons_BanAnd no definition is necessary. More than 600 individual models and various features were included in the law. And it was found to be legal.
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