A firm that distributed 3D-printer blueprints for guns has circumvented a ban on sharing them online by selling flash drives containing the files.
The designs had been available for free download but a temporary ban was imposed by a US judge concerned that they could fall into the wrong hands.
Defense Distributed now promises to deliver the drives to customers in select states.
Its suggested price is $10 (£7.70), but customers can choose how much to pay.
The history of what the Texas-based firm's founder Cody Wilson calls the "downloadable gun" has been a chequered one.
The computer-aided designs (CADs) were originally published online in 2013. But the website was quickly ordered to remove the files over fears they could be used by terrorists or criminals to make untraceable "ghost guns".
In a surprise move, and following lengthy court action from Defense Distributed, the US Department of Justice ruled in July that the blueprints did not represent a national security threat and could be put back online.
They were downloaded thousands of times, prompting outcry from 19 US states. Led by Washington state, they launched a legal action against the US government.
That in turn led to a federal judge issuing a temporary ban which saw the files once again removed from the internet.
Now back online, the files are only available for purchase for delivery to customers based in states that have not imposed a ban.
Those living elsewhere are told: "Your masters say you can't be trusted with this information."
Users can also submit their own files to sell on the platform and will get a 50% cut.
At a news conference, Mr Wilson said his firm had already received 400 orders.
"I'm happy to become the iTunes of 3D guns if I can't be the Napster", the news site Ars Technica reported him as saying.
Napster was a file-sharing music service, which offered MP3s for free.
"Anyone who wants to get these files is going to get them. They can name their own price," Mr Wilson added.
He said that his move was motivated by the desire to support freedom of speech rather than to make money.
The main Defense Distributed website still carries a statement saying that it had been ordered to shut down its file repository.
Defense Distributed's files cover a range of firearms, including 3D-printable components that could make a version of the AR-15 rifle, a gun that has been used in US mass shootings.