Editor’s Note: This article was originally published by Cato.org and is republished here with permission.

By: Ilya Shapiro and Matthew Larosiere Share

A Massachusetts statute prohibits ownership of “assault weapons,” the statutory definition of which includes the most popular semi-automatic rifles in the country, as well as “copies or duplicates” of any such weapons.

As for what that means, your guess is as good as ours. A group of plaintiffs, including two firearm dealers and the Gun Owners’ Action League, challenged the law as a violation of the Second Amendment. Unfortunately, federal district court judge William Young upheld the ban.

Judge Young followed the lead of the Fourth Circuit case of Kolbe v. Hogan (in which Cato filed a brief supporting a petition to the Supreme Court) which misconstrued from a shred of the landmark 2008 District of Columbia v. Heller case that the test for whether a class of weapons could be banned was whether it was “like an M-16,” contravening the core of Heller — that all weapons in common civilian use are constitutionally protected.

What’s worse is that Judge Young seemed to go a step further, rejecting the argument that an “M-16” is a machine gun, unlike the weapons banned by Massachusetts, and deciding that semi-automatics are “almost identical to the M16, except for the mode of firing.” (The mode of firing is, of course, the principle distinction between automatic and semi-automatic firearms.)

The plaintiffs are appealing to the U.S. Court of Appeals for the First Circuit. Cato, joined by several organizations interested in the protection of our civil liberties and a group of professors who teach the Second Amendment, has filed a brief supporting the plaintiffs. We point out that the Massachusetts law classifies the common semi-automatic firearms used by police officers as “dangerous and unusual” weapons of war, alienating officers from their communities and undermining policing by consent.

Where for generations Americans needed look no further than the belt of their local deputies for guidance in selecting a defensive firearm, Massachusetts’ restrictions prohibit these very same arms from civilians. Those firearms selected by experts for reliability and overall utility as defensive weapons, would be unavailable for the lawful purpose of self-defense. According to Massachusetts, these law enforcement tools aren’t defensive, but instead implements of war designed to inflict mass carnage.

Where tensions between police and policed are a sensitive issue, Massachusetts sets up a framework where the people can be fired upon by police with what the state fancies as an instrument of war, a suggestion that only serves to drive a wedge between police and citizenry.

Further, the district court incorrectly framed the question as whether the banned weapons were actually used in defensive shootings, instead of following Supreme Court precedent and asking whether the arms were possessed for lawful purposes (as they unquestionably were). This skewing of legal frameworks is especially troublesome where the Supreme Court has remained silent on the scope of the right to keep and bear arms for the last decade, leading to a fractured and unpredictable state of the law.

Today, the majority of firearms sold in the United States for self-defense are illegal in Massachusetts. The district court erred in upholding this abridgment of Bay State residents’ rights. The Massachusetts law is unconstitutional on its face and the reasoning upholding it lacks legal or historical foundation.