The Biden ATF’s war on pistol braces is over. On July 17, 2025, the Trump Department of Justice filed a stipulation of dismissal in the Fifth Circuit, dropping the government’s appeal in Mock v. Bondi — formerly Mock v. Garland. That single filing makes permanent Judge Reed O’Connor’s nationwide vacatur of ATF Final Rule 2021R-08F, 88 Fed. Reg. 6,478 (Jan. 31, 2023), the Biden-era rule that would have reclassified millions of brace-equipped pistols as short-barreled rifles subject to the National Firearms Act. This is a clean, decisive win for the Second Amendment and a serious blow to administrative overreach by the ATF.
What Judge O’Connor Actually Did — and Why It Matters
This is not just an injunction. Judge Reed O’Connor of the U.S. District Court for the Northern District of Texas (Fort Worth Division) entered something more powerful: vacatur under the Administrative Procedure Act, 5 U.S.C. § 706(2). Vacatur is technically distinct from a traditional injunction. It does not merely block enforcement against specific parties — it nullifies the rule ab initio, meaning the rule is treated as if it never existed at all.
O’Connor’s June 13, 2024 opinion was scathing. He found the ATF had engaged in arbitrary and capricious rulemaking when it reversed nearly a decade of settled agency practice without adequate explanation. His words are worth quoting at length:
“For close to a decade, the ATF concluded that attaching the brace to a firearm does not alter the classification of the firearm or subject the firearm to NFA control. The ATF changed course on this position for the first time in 2023 when it issued the final rule reversing the ATF’s otherwise long-standing policy. When an agency changes course, as the ATF did here, it must be cognizant that long-standing policies and practices may have engendered serious reliance interests that must be taken into account. It would be arbitrary and capricious to ignore such matters.”
He went further, noting that under the final rule the ATF estimated 99% of braced pistols would be reclassified as NFA rifles — and that even the Fifth Circuit could not identify a single example of a braced pistol that would qualify for the NFA exemption. That level of regulatory incoherence is textbook arbitrary and capricious.
Vacatur Ab Initio: The Right Remedy for an Unlawful Rule
On the remedy question, O’Connor was equally clear:
“An illegitimate agency action is void ab initio and therefore cannot be remanded as there is nothing for the agency to justify… . There are meaningful differences between an injunction — which is a drastic and extraordinary remedy — and vacatur — which is a less drastic remedy. Vacatur does nothing but reestablish the status quo that existed for decades prior to the final rule going into effect.”
My read is that this framing is critical. By entering nationwide vacatur rather than a plaintiff-limited injunction, O’Connor treated the Biden brace rule as legally non-existent. The Trump DOJ’s dismissal of the Fifth Circuit appeal locks that remedy in permanently. There is no live appeal left to reinstate the rule.
FPC, William Mock, and the People Who Won This Fight
The plaintiffs in this case — lead plaintiff William Mock, the Firearms Policy Coalition (FPC), and Maxim Defense Industries — deserve real credit. Brandon Combs, founder and president of FPC, put it plainly:
“Today is a great day for freedom and the American people. The dismissal of this appeal should be the final nail in the coffin of this unconstitutional Biden ATF assault on gun owners. As we explained in the case filings, braced pistols are not short barrel rifles. But either way, they are unquestionably arms protected under the Second Amendment. We are thrilled to have secured this important win for liberty.”
David Farrell of Maxim Defense and lead outside counsel Brad Benbrook of the Benbrook Law Group in Sacramento were also central to getting this case across the finish line. This is exactly the kind of coordinated, well-executed Second Amendment litigation that produces durable results.
Could a Future Administration Bring the Rule Back?
Theoretically possible, practically very difficult. Any administration that wanted to revive a brace rule would have to write a completely new rule from scratch — one that survives APA arbitrary-and-capricious review after O’Connor’s thorough dismantling of the original. That is a steep bar.
More importantly, the NFA tax on short-barreled rifles, short-barreled shotguns, and suppressors has already dropped to zero effective January 1, 2026. My read is that demand will explode as these items enter the market without the $200 tax burden. Once braced pistols and SBRs are indisputably in common use by Americans for lawful purposes, the constitutional protection becomes airtight under Heller and Bruen — and any future effort to reclassify them hits a second wall on top of the APA one.
Closing
The Biden pistol brace rule — Final Rule 2021R-08F, 88 Fed. Reg. 6,478 — is void ab initio. The Trump DOJ made the right call. Congratulations to William Mock, Brandon Combs and FPC, David Farrell and Maxim Defense, and Brad Benbrook. This is what winning looks like.
This article is based on analysis by Professor Mark W. Smith, constitutional attorney and Host of the Four Boxes Diner 2nd Amendment channel. Watch the original video here. This does not constitute legal advice.