America's highest judicial body heard arguments late last year over whether the Biden administration was illegally expanding the definition of "firearm" to include "partially completed pistol frames."

In stunning development, all of the Supreme Court justices appointed by President Donald Trump found that the new definition is lawful. 

Case concerned ATF Final Rule 2021R-05F

According to Breitbart, then Solicitor General Elizabeth Prelogar defended the change, which was implemented by the Bureau of Alcohol, Tobacco and Firearms (ATF).

Known as ATF Final Rule 2021R-05F, it was signed by then Attorney General Merrick Garland in April of 2022 and was meant to address "technological advancements and judicial developments since the regulatory definitions were originally set forth in 1968 and 1971."

FPC LEGAL ALERT: The Supreme Court has upheld the ATF's "frame or receiver" rule. You can read the opinion here: https://t.co/qcBmmWGcBX pic.twitter.com/uMCAxV9gUq

— Firearms Policy Coalition (@gunpolicy) March 26, 2025

The rule categorized as a firearm any "partially complete, disassembled, or nonfunctional frame or receiver that has reached a stage in manufacture where it may quickly and easily ('readily') be made to function as a 'frame or receiver.'"

Solicitor general said change was consistent with past definitions

During oral arguments this past October, Prelogar maintained that the new definition is not a departure from how the federal government has defined firearms hitherto.

"We think the context and purpose of the statute strongly support understanding the term in this way," Breitbart quoted her as saying.

"And the reason for that is because, throughout the federal firearms laws, whenever Congress has itself expressly provided a definition, it has included not only the fully complete and functional item but things that are the item and can readily be made to function that way," she added.

However, Breitbart noted that Justice Samuel Alito sounded deeply skeptical regarding the way that Prelogar likened a weapon to its components.

Justice Alito asked if a pad and a pen are the same as a grocery list

"Here is a blank pad and a pen," the Republican-appointed justice remarked to Prelogar before asking, "Is this a grocery list?"

Prelogar responded that it was not as there are multiple alternative uses for Alito's pen and paper aside from creating a grocery list.

"If I put on a counter some eggs, some chopped up ham, some chopped up pepper and onions, is that a western omelet?" Alito went on to ask.

The then solicitor general again said that such ingredients do not constitute an omelet on their own as there are "well-known other uses" for them.