The company behind the plans, Defense Distributed, reached an agreement with the federal government in June allowing it to make the plans for the guns available for download, starting this week.
US District Judge Robert Lasnik issued a temporary restraining order halting the release hours before the 1 August deadline, saying the blueprints could fall into the wrong hands. The single-shot pistol was made nearly entirely out of ABS plastic - the same material Lego bricks are made from - and could be made on a 3D printer.
Gun control advocates say downloadable guns undermine laws that block unsafe people from accessing firearms.
Before the settlement with the Trump administration, Wilson had lost in both district and appellate court.
But it is unclear how effective the temporary restraining order is since the schematics for one of its guns - The Liberator - were posted on the company's website on Friday - five days ahead of the company's announced release date.
One website, CodeIsFreeSpeech.com, posted eight sets of files and reported more than 100,000 hits and almost 1.5 terabytes of data downloaded by 6 a.m. Wednesday. The settlement allowed the company to distribute its blueprints online.
Unless money is no object for an owner, 3D-gun printing might be considered by some a cost-prohibitive endeavor that's more hard than simply buying a gun.
Lasnik explained the ruling by saying that there was a "possibility of irreparable harm because of the way these guns can be made", noting that they are not traceable. He understands concerns about the guns' ability to be detected, but laws already make it illegal for people to possess undetectable guns. The "ghost guns" blueprints have already been downloaded thousands of times since they were leaked online this week.
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State Department officials said their only role was to prohibit export of the blueprints outside the U.S. "The introduction of 3D technology will change that completely because now people will have the capacity to build guns on their own, which will be totally off the grid".
Defense Distributed and its founder Cody Wilson, a self-declared anarchist, argued that access to the online blueprints is guaranteed under First and Second Amendment rights which confer the right to free speech and to bear arms.
"It is immediately obvious to anyone who looks at this issue that 3D-printed guns are nothing short of a menace to society, and we are thrilled that the court ruled in this manner", stated Avery Gardiner, co-president of the Brady Campaign.
One gun made with a plastic called ABS-M30 fired a.380-caliber round without failing all eight times it was tested, ATF officials said, describing it as "a lethal weapon".
Plastic gun designs got around this restriction by adding a removable metal block, which isn't required for the firearm to function.
It would have allowed anyone with access to a printer to potentially build a lethal weapon, which opponents say can not be seen by a metal detector or tracked to a licence holder.
"If somebody walked in here with a 3D-printed gun, I'd be like 'Get out of here".
