Supreme Court Holds ATF Rule on Weapon Parts Kits and Unfinished Frames Is Not Facially Inconsistent With the Gun Control Act

The decision

On March 26, 2025, the Supreme Court of the United States reversed a judgment of the United States Court of Appeals for the Fifth Circuit that had set aside two provisions of a 2022 rule adopted by the Bureau of Alcohol, Tobacco, Firearms and Explosives. The rule treats certain weapon parts kits, and certain partially complete frames and receivers, as firearms subject to the Gun Control Act of 1968. In an opinion by Justice Gorsuch for seven Justices, the Court held that the rule is not facially inconsistent with the Act because the statute reaches at least some kits and at least some unfinished frames or receivers. The Court stated that the case, as presented, did not ask whether the regulations may lawfully be applied to particular products. Justices Sotomayor, Kavanaugh and Jackson filed concurring opinions; Justices Thomas and Alito each filed dissents.

Background

The Gun Control Act requires many importers, manufacturers and dealers in firearms to obtain federal licenses, keep sales records and conduct background checks, and requires importers and manufacturers to mark firearms with serial numbers. Section 921(a)(3) of Title 18 defines a firearm to include, in subsection (A), any weapon, including a starter gun, that will, is designed to, or may readily be converted to expel a projectile by the action of an explosive, and, in subsection (B), the frame or receiver of any such weapon.

According to the opinion, companies now sell weapon parts kits that individuals assemble into functional firearms at home, and the kits vary widely in completeness and in the work required to finish them. In 2022, ATF adopted a rule under 18 U.S.C. § 926(a). One provision, 27 CFR § 478.11, defines a firearm to include a weapon parts kit that is designed to or may readily be completed, assembled, restored or otherwise converted to expel a projectile by the action of an explosive. Another, § 478.12(c), defines a frame or receiver to include a partially complete, disassembled or nonfunctional frame or receiver that is designed to or may readily be converted to function as one.

Before the rule took effect, gun manufacturers, at-home gunsmiths and others filed what they described as a facial challenge under the Administrative Procedure Act in the United States District Court for the Northern District of Texas, arguing that the two provisions had to be set aside as issued in excess of statutory authority under 5 U.S.C. § 706. The district court granted summary judgment to the plaintiffs and vacated the rule. The Fifth Circuit largely affirmed, holding that subsection (A) categorically does not reach weapon parts kits regardless of completeness or ease of assembly, and that subsection (B) reaches only finished frames and receivers.

The court’s reasoning

The scope of the challenge

The plaintiffs pursued a facial pre-enforcement challenge to ATF’s authority to regulate any kits or unfinished frames or receivers. The government argued, citing INS v. National Center for Immigrants’ Rights, Inc., that the possibility a regulation may be invalid as applied in some cases does not make it facially invalid, and that the plaintiffs had to show the rule itself is inconsistent with the statute on its face. Because the plaintiffs did not dispute that framing, the Court took it as given, and in a footnote declined to address the dissents’ questions about the proper test, stating that those theories were not pressed below or before the Court.

Weapon parts kits

The Court read subsection (A) to impose two requirements: a weapon must be present, and it “must be able to expel a projectile by the action of an explosive, designed to do so, or susceptible of ready conversion to operate that way.” It worked from a record example, Polymer80’s “Buy Build Shoot” kit, which contains all components needed to build a Glock-variant semiautomatic pistol and which, in an ATF test, a person who had never encountered it assembled into a gun in 21 minutes using common tools.

Three considerations persuaded the Court that the kit is a weapon. First, the term is “an artifact noun—a word for a thing created by humans,” and ordinary speakers use such nouns for unfinished objects when their intended function is clear. Second, the statute says a weapon includes a starter gun, which normally fires blanks and requires conversion work. Third, the “designed to” and “readily be converted” clauses necessarily contemplate items short of fully operable firearms. On the second requirement, the Court reasoned that because a person without specialized knowledge can convert a starter gun with everyday tools in under an hour, and the kit requires no more time, effort, expertise or specialized tools, the kit is readily convertible as well.

The Court acknowledged that some kits may be so incomplete or cumbersome to assemble that they cannot fairly be called weapons capable of ready conversion, and declined to decide how far subsection (A) reaches. “Because at least some weapon parts kits satisfy both of subsection (A)’s tests, § 478.11 is not facially invalid.” The Court also rejected the plaintiffs’ arguments that Congress’s express treatment of combinations of parts elsewhere excludes kits and that kits cannot be weapons because they lack functional frames or receivers.

Frames and receivers

On § 478.12(c), the Court stated that the Act “reaches, and permits ATF to regulate, at least some” partially complete frames or receivers. Its example was a Polymer80 Glock-variant frame that differs from a completed frame mainly by plastic tabs a novice can remove within minutes with common tools. The Court reasoned that frame and receiver are artifact nouns; that § 923(i)’s serialization mandate uses the same words for items, such as silencers, that lack finished frames, and that the same words a few sections apart should carry the same meaning, citing Azar v. Allina Health Services; and that ATF has for decades read subsection (B) to reach some unfinished frames, a consistent practice that, under Loper Bright Enterprises v. Raimondo, may provide evidence of meaning though courts exercise independent judgment. The Court also relied on the plaintiffs’ statement at argument that they have no “quarrel” with ATF’s “prior practice.”

The Court found unpersuasive the argument that subsection (B) omits the ready-conversion language of subsection (A), reasoning that unadorned artifact nouns can describe unfinished articles and that subsection (B)’s reference to “any such weapon” incorporates subsection (A)’s definition. On the plaintiffs’ warning that the reasoning could lead ATF to treat AR–15 receivers as machinegun receivers under the National Firearms Act, the Court noted the government’s representation that they do not so qualify and stated: “Our analysis of the GCA thus does not begin to suggest that ATF possesses authority to regulate AR–15 receivers as machineguns under the NFA.” It left the plaintiffs’ objection to ATF’s consideration of jigs, tools and instructions “for another day.”

Lenity and avoidance

The Court declined to apply the rule of lenity or constitutional avoidance, stating that neither has a role where “text, context, and structure” decide the case, citing Van Buren v. United States.

Separate opinions

Justice Sotomayor, concurring, responded to Justice Kavanaugh’s concern about compliance uncertainty: “That worry is unfounded.” She wrote that regulated entities have complied with the Act for more than half a century and may seek classification decisions from ATF. Responding to Justice Alito’s description of the holding, she wrote: “I encourage readers to go to the source, rather than rely on dissents, to understand what the Court holds.”

Justice Kavanaugh, concurring, wrote that a good-faith actor may have difficulty determining when kits or unfinished frames qualify: “The line is not entirely clear.” He noted that licensing, recordkeeping and serialization violations are punishable only if willful, and that background-check violations require only knowledge, which he said could raise fair-notice concerns.

Justice Jackson, concurring, wrote that excess-of-authority review “must focus on actual statutory boundaries,” and that where those boundaries do not foreclose the agency’s action the claim should fail.

Justice Thomas, dissenting, wrote: “The Government now asks us to rewrite statutory text so that it can regulate weapon-parts kits. This time, the Court obliges. I would not.” He wrote that the facial-challenge framework “seems plainly inapt” in a challenge to a regulatory definition, and argued that Congress omitted the ready-conversion and combination-of-parts language from subsection (B) and that the artifact-noun approach substitutes colloquial usage for traditional interpretation. He would apply the rule of lenity, drawing on United States v. Thompson/Center Arms Co.

Justice Alito, dissenting, wrote that the Court decided the case on a ground not raised below and that he would have joined the Court’s opinion if satisfied that the Salerno test controlled: “But I am not certain that the Salerno test should govern.” He argued that the test’s rationale of respecting legislative authority does not apply to regulations and that he would either order briefing on the issue or vacate and remand.

Status

The Court reversed the Fifth Circuit’s judgment and remanded for further proceedings, stating that the parties may not raise on remand arguments about the proper test that they did not pursue before the Court. The Court did not decide whether the rule may be applied to any particular product, what weight ATF may give jigs, tools and instructions, or the proper standard for pre-enforcement APA challenges.

The decision was widely reported on the day it issued, including by NPR, the Associated Press, Reuters, CNN, The Washington Post, CBS News, ABC News and SCOTUSblog.