In a 7-2 decision, the U.S. Supreme Court on Wednesday upheld an ATF rule promulgated under the Biden administration that treats unfinished frames and receivers and DIY-gunmaking kids as fully functional firearms subject to federal law, overturning the Fifth Circuit Court of Appeals and holding that the regulation is not "facially inconsistent with the Gun Control Act."

Justices Thomas and Alito dissented from the majority opinion, which was authored by Justice Neil Gorsuch. In the majority opinion, Gorsuch explains why the rule passes muster; not from a Second Amendment standpoint, which was never the focus of the plaintiffs' arguments, but under the Administrative Procedures Act:

Before ATF could enforce its rule, gun manufacturers and others filed what they described as a facial challenge under the Administrative Procedure Act, arguing that the GCA cannot be read to reach weapon parts kits or unfinished frames or receivers. The District Court agreed and vacated the rule. The Fifth Circuit affirmed, holding that §921(a)(3)(A) categorically does not reach weapon parts kits regardless of completeness or ease of assembly, and that §921(a)(3)(B) reaches only finished frames and receivers. 

(a) Section 478.11’s provisions addressing weapon parts kits are not facially invalid under §921(a)(3)(A). That subsection contains two requirements: a “weapon” must be present, and that weapon 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. Some weapon parts kits meet that description. Consider, for instance, Polymer80’s “Buy Build Shoot” kit, which contains all necessary components to build a semiautomatic pistol and can be assembled in about 20 minutes using common tools. That kit qualifies as a “weapon” because: (1) artifact nouns like “weapon” often describe unfinished objects when their intended function is clear, as with a disassembled rifle; (2) the statute treats starter guns as weapons though they require conversion work; and (3) the statutory text contemplates that some things short of fully operable firearms qualify as “weapons.” The kit also satisfies the statute’s second requirement, as it requires no more time, expertise, or specialized tools to complete than a starter gun ,which the statute treats as readily convertible into a functioning firearm. While other kits may be so incomplete or cumbersome to assemble that they cannot fairly be described as weapons capable of ready conversion, the facial challenge fails because kits like Polymer 80’s clearly qualify.

Remember, under a facial challenge the rule must be found to always violate a particular statute; in this case the APA. Even after today's decisions manufacturers could bring an as applied challenge to the rule, and the Trump administration could also formally repeal the rule on its own. 

What about treating unfinished frames and receivers as functional firearms, even if they're not sold as part of a larger kit?

(b) Section 478.12(c)’s treatment of partially complete frames and receivers is also not facially invalid under §921(a)(3)(B). Like “weapon,” the artifact nouns “frame” and “receiver” may describe not yet-complete objects. The statute uses these terms to encompass some unfinished items elsewhere, as in §923(i)’s serialization requirements for incomplete weapons, silencers, and destructive devices. ATF has for decades interpreted the statute to reach some unfinished frames and receivers, and even the plaintiffs concede they have no “quarrel” with ATF’s prior practice of regulating those products. Accordingly, the statute authorizes ATF to regulate at least some incomplete frames or receivers that take minutes of work with common tools to complete. While other products may be so far from finished that they cannot fairly be described as frames or receivers, the facial challenge fails because the statute plainly reaches some partially complete items.

Is there any good news for Second Amendment advocates in the opinion? Well, yes, or at least maybe. 

There goes one argument that some gun control groups have been recently trying to make in court https://t.co/30LVL8Djlk pic.twitter.com/0Hfufiibes

— Rob Romano (@2Aupdates) March 26, 2025

If unfinished frames and receivers can be treated as fully functional firearms because they can be converted into such, what's stopping the Supreme Court (or lower courts) from adopting the arguments of anti-gunners that semi-automatic firearms should be treated like machine guns because they too can be converted to full-auto? 

That result, the plaintiffs warn, could leave many Americans facing new and unforeseen criminal liability for possession of a “machinegun” simply because they own a “popular” and “commonly available” rifle. The plaintiffs’ fears are misplaced. The government represents that AR–15 receivers do not “qualify as the receiver of a machinegun.” Nor, the government emphasizes, has ATF ever “suggested otherwise.” Much the same can be said of our reasoning today. As we have stressed, a statute’s text and context are critical to determining whether (and to what extent) Congress used an artifact noun to reach unfinished objects. And, without doubt, the NFA and the GCA are different statutes passed at different times to address different problems using different language. 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.

With all due respect to Gorsuch, he and his fellow justices have also stated that the Second Amendment isn't a second-class right, but that hasn't stopped lower court judges from treading all over our right to keep and bear arms. Similarly, today's note of caution about treating semi-automatic firearms as "machineguns" may very well be disregarded by lower courts going forward. That's one reason why SCOTUS needs to address semi-auto bans and declare them an affront to the Constitution and the Second Amendment. 

In his dissent, Justice Clarence Thomas took issue with multiple aspects of the majority opinion, including its assertion that gun-making kits can be treated as completed firearms under the GCA. 

The text, context, and structure of §921(a)(3) leave little doubt that weapon-parts kits are not “firearms,” and that the unfinished contents of these kits are neither “frame[s]” nor “receiver[s].” But, even if it were reasonable to treat artifact nouns differently, the Government would—at most—demonstrate statutory ambiguity. And, when a statute with criminal applications is ambiguous, the rule of lenity applies.

... Nothing in the GCA suggests that the terms “frame” and “receiver” also include the materials that one could use to create them, or that parts including neither a frame nor a receiver could constitute a “weapon.” There are, however, many reasons to conclude the opposite. Even the Government appears to have found these competing interpretations persuasive just a few years ago. See Brief for ATF 14, 36–39 (endorsing the position it now rejects). “Now it says the opposite. The law hasn’t changed, only an agency’s interpretation of it.” 

... Congress could have authorized ATF to regulate any part of a firearm or any object readily convertible into one. But, it did not. I would adhere to the words Congress enacted. Employing its novel “artifact noun” methodology, the majority charts a different course that invites unforeseeable consequences and offers no limiting principle. I respectfully dissent.

In his own dissent, Justice Samuel Alito argued the Court "decides this case on a ground that was no traised or decided below and that was not the focus of the briefing or argument in this Court", opining that that this wasn't a true facial challenge as presented by the plaintiffs. But in a footnote, he also took pains to point out what he believes is the limited nature of today's ruling.

JUSTICE SOTOMAYOR’s suggestion that I have mischaracterized what the Court has held demands a response. Although JUSTICE SOTOMAYOR obviously wishes that the Court had gone further, all that the Court has actually held is that the ATF rule is not facially invalid because at least some applications of the rule are consistent with the statute. And the two examples that the Court cites are (1) a kit that contains all the parts needed to make a semiautomatic pistol and that can be assembled in 21 minutes, and (2) a frame that can be made functional simply by clipping off two plastic tabs and drilling a few holes. The Court has not held that any other kits or presently non-functional receivers are covered.

This is obviously not the decision Second Amendment advocates were hoping for, and as Thomas says, it opens the door for unforeseeable consequences in the future; if not under the Trump administration then the next time a Democrat president once again weaponizes the ATF to target gun owners and the firearms industry. President Trump can blunt today's decision by formally repealing the "frame and receiver" rule, but that won't stop a future administration from putting it (or something far worse) in place in the future.