In a huge blow to President Joe Biden’s bid to ban “assault weapons,” a federal court today ruled that the administration’s effort to regulate and tax AR-15 style “pistols” is “unlawful” and “illegitimate.”

In a 12-page decision, the Texas-based U.S. District Court vacated the rule that could have led to the destruction of millions of firearms, among the most popular in America, and the jailing of owners who had refused to comply with the administration.

The court also blasted the Bureau of Alcohol, Tobacco, Firearms and Explosives for thinking that it could change a long-established exemption overnight to make ownership of the firearms illegal.

In reacting to the case, Mock vs. Garland, the Firearms Policy Coalition, which pushed the case, tweeted out what it called the “layman’s” summary.

“ATF broke the law by being overreaching sneaky pricks. Therefore, the right thing for the Court to do was throw the Rule in the trash. The Court threw the Pistol Brace Rule in the trash,” it said.

The same court had earlier approved the ATF rule, but an appeals court overruled it. In today’s decision, the District Court judge agreed that the ATF rule was illegal and likely to be rejected by other courts.

The case is likely headed to the U.S. Supreme Court, those involved said.

For now, it is legal to have the pistols — AR style or others — equipped with stabilizing arm braces.

For years, ATF gave its blessing that putting the adjustable braces on pistols was allowed even though the braces could be used as a style of stock, turning the firearms into short-barreled rifles. Typically, short barreled rifles are regulated under the Al Capone era National Firearms Act which requires a $200 tax stamp and registration.

In his decision, Judge Reed O’Connor said that the ATF was wrong in just changing its mind without giving an explanation. He also hit the agency for ignoring comments from users and writing the rule vaguely.

“The court finds that the adaptation of the final rule was arbitrary and capricious for two reasons. First, the defendants did not provide a detailed justification for their reversal of the agency’s longstanding position. And second, the final rule’s standards are impermissibly vague,” wrote the judge.

There are an estimated 10 million or more of the firearms in America. During an ATF grace period, when owners were allowed to register their weapons free of the $200 tax, less than 300,000 did so.

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The firearms are popular for plinking at ranges and for self-defense because they are smaller than a traditional AR-15 rifle. Many have barrels about half the length of a traditional rifle, and the pistol brace stock is adjustable.

The administration pushed the rule by claiming the guns were the choice in mass shootings, though just a few have been used in those events.