Bondi

Majority — Gorsuch

Joined by: Roberts, Sotomayor, Kagan, Kavanaugh, Barrett, Jackson

The majority held that the Gun Control Act's definition of "firearm" is broad enough to cover at least some weapon parts kits and some partially complete frames or receivers, so the ATF's rule cannot be thrown out entirely. The Court reasoned that words like "weapon," "frame," and "receiver" are artifact nouns — words for human-made objects — and that ordinary speakers sometimes use such words to describe unfinished versions of those objects when their intended purpose is obvious, just as someone might call an unassembled IKEA kit a "table." Using the Polymer80 "Buy Build Shoot" kit as an example — a kit containing all parts needed to build a pistol, assembled by a first-time user in 21 minutes with common tools — the Court found it clearly qualifies as a "weapon" capable of "ready conversion" into a working firearm, especially since the statute already treats starter guns (which also require conversion work) as weapons. The Court applied the same logic to partially complete frames, noting that the GCA's serialization rules already use the word "frame" to cover unconventional and unfinished items, and that ATF had for decades regulated some unfinished frames without objection from the plaintiffs themselves. Because at least some kits and frames fall within the statute's reach, the Court said the rule cannot be struck down as facially invalid — meaning invalid in every possible application — and left harder line-drawing questions for future cases.

Dissent reasoning

Justice Thomas, joined by no other Justice, argued that the majority misread the statute and applied the wrong legal standard. In his view, the terms "frame" and "receiver" in the GCA have clear ordinary meanings — the finished, functional structural components of a gun — and an object that must still be converted into a frame or receiver is not yet one, just as a caterpillar is not yet a butterfly. He pointed out that Congress deliberately narrowed the GCA's predecessor law, which had covered "any part or parts" of a firearm, down to only "the frame or receiver," and that this deliberate narrowing should be respected. Thomas also argued that the majority's "artifact noun" linguistic theory is a novel substitute for traditional statutory interpretation, and that casual conversational usage should not drive the meaning of precise legal text. He further warned that the majority's reasoning could have sweeping unintended consequences: because the National Firearms Act defines "machinegun" to include the "frame or receiver of any such weapon," and because AR-15 receivers can be converted to fire automatically, the majority's logic could expose millions of AR-15 owners to criminal liability as possessors of unregistered machineguns. Thomas would have applied the rule of lenity — a legal principle requiring courts to resolve ambiguous criminal statutes in favor of the defendant — and ruled against the ATF. Justice Alito dissented separately, arguing on procedural grounds that the Court should not have applied the demanding "facial challenge" legal standard (drawn from United States v. Salerno) without full briefing and argument on whether that standard even applies to challenges against agency regulations, since doing so effectively makes it nearly impossible to strike down an agency rule in its entirety.