First Circuit Upholds Denial of Preliminary Injunction Against Massachusetts’ Ban on Assault Weapons and Large-Capacity Magazines

By V.R. Bohman and Jesse Hogin

In April 2025, the U.S. Court of Appeals for the First Circuit decided Capen v. Campbell, a case arising from a challenge to Massachusetts’ ban on assault weapons and large-capacity magazines. The court affirmed a district court’s denial of a motion for preliminary injunction against the ban, holding that (1) Massachusetts had shown that the assault-weapon ban comports with historical firearm regulation; and (2) First Circuit precedent dictated that the large-capacity-magazine ban most likely does the same.¹ The court also made clear, however, that its “affirmance of the denial of the PI motion does not end the case; future developments in the record (and in the parties’ arguments) may possibly warrant a different outcome beyond the preliminary-injunction stage.”² Capen joins a host of Second Amendment cases that stakeholders should keep close tabs on.

Background

The Massachusetts ban criminalizes the sale, transfer, or possession of “an assault weapon or a large capacity feeding device” not lawfully possessed before September 13, 1994.³ The ban defines “assault weapons” to match the now-expired federal definition of “semiautomatic assault weapon” and to include several specific firearms.⁴ The ban defines “large capacity feeding device” to match the now-expired federal definition of the same term and as a magazine or similar that can hold more than ten rounds of ammunition or more than five shotgun shells.⁵

The plaintiffs — an individual gun owner and the National Association for Gun Rights — alleged that the ban violates the Second Amendment both facially and as applied “to law-abiding adults seeking to . . . possess arms that are in the common use by the American public for lawful purposes.”⁶ They also requested both a preliminary and permanent injunction against the ban’s enforcement.⁷ The district court denied the plaintiffs’ motion for preliminary injunction, concluding that the plaintiffs were unlikely to succeed on the merits.⁸

First Circuit Opinion

The court first analyzed the plaintiffs’ standing to sue. For the gun owner, the court held that his allegation that he would buy a banned firearm but for the credible threat of prosecution was sufficient injury.⁹ For the association, the court held that standing “is murkier” because the association failed to name any member the ban affected.¹⁰ But the court did not dismiss the association because if at least one plaintiff has standing (the gun owner), a case may proceed and because the association could amend its complaint after the First Circuit decided the preliminary-injunction appeal.¹¹

The court then turned to the assault-weapon ban. But before applying the framework to assess the ban’s legality, the court made three preliminary observations: (1) it need only to determine whether the ban comports with the United States’ “historical tradition” of firearm regulation, as an affirmative finding on that issue makes plaintiffs’ success on the merits unlikely; (2) this case requires “a more nuanced approach” to historical-tradition analysis because of “the contemporary and growing societal concern of mass shootings”; and (3) because the plaintiffs challenged the ban “on [its] face” and focused “almost exclusively” on the AR-15 in their arguments, the court would focus its analysis on that firearm.¹²

The court’s “nuanced approach” comprised comparing “how and why” the ban burdens a citizen’s right to armed self-defense against “how and why” historical regulations burdened the same.¹³ For the “how,” the court held that the AR-15 ban is not a heavy burden on self-defense, noting that the plaintiffs failed to “demonstrate a single instance where the AR-15 . . . has actually been used in a self-defense scenario”, and that Massachusetts showed that the AR-15 “offers limited self-defense utility.”¹⁴ The court also rejected the plaintiffs’ argument that firearms “in common use” (by statistics) cannot be banned because, the court noted, the Supreme Court “has not held that states may permissibly regulate only unusual weapons.”¹⁵ The court then determined it was bound by circuit precedent that discussed historical bans on gun powder, trap guns, and machine guns and held that “it . . . seems reasonably clear that our historical tradition of regulating arms used for self-defense has tolerated” burdens similar to those posed by the AR-15 ban.¹⁶

For the “why,” the court noted support in the record for Massachusetts’ argument that the ban’s “manifest purpose” was to “make[] it harder for criminals to get their hands on . . . dangerous guns.”¹⁷ The court rejected the plaintiffs’ argument that “mass shootings are . . . relatively rare” and do not justify the ban.¹⁸ The court rejected this argument, stating the sole question was “whether [the ban’s purpose] is analogous to” that of historical regulations, not whether the ban’s asserted justifications were legitimate.¹⁹ The court also held that other regulations such as those on sawed-off shotguns and Bowie knives “reflect a common concern regarding the State’s responsibility to protect the public from the danger caused by weapons that create a particular public safety threat.”²⁰ The court then held — putting these “how and why” comparisons together — that Massachusetts had “at least preliminarily demonstrated that” the AR-15 ban “is part of the historical tradition that delimits the outer bounds of the right to keep and bear arms.”²¹

The court next turned to the large-capacity-magazine ban. The court held — and the plaintiffs conceded — that its precedent (analyzing “an almost identically worded” Rhode Island ban on large-capacity magazines) dictated that applying the framework to assess the ban’s legality “strongly points in the direction of finding that [the] ban does not violate the Second Amendment.”²²

For these reasons, the court held that the plaintiffs were unlikely to succeed on the merits — for both the assault-weapon and large-capacity-magazine bans — and thus the district court properly denied their motion for preliminary injunction.²³