Court rules the First Amendment does not apply to speech about guns
There are a couple problems with this ruling. The most obvious is that the First Amendment doesn't have a national security exception. People can agree not to disclose classified information (such as in return for employment or access to the information), and that agreement can be enforced, but the government can't go to a newspaper and say they aren't allowed to publish something classified. They can ask nicely and most journalists will play along if it's really about national security, but that's it. And this isn't about national security; it's about the ability to 3D-print a very basic handgun. There are millions of handguns legally owned in the United States and probably billions in the world.
Second, this has already been litigated. Decades ago, when BJ Clinton was president, there was a program called Pretty Good Privacy that was able to encrypt messages in a way that the government could not decrypt. The government hated that program and wanted it destroyed. If they couldn't have it destroyed, they wanted to make sure it stayed within the borders of the United States. They had regulations about that, regulations that treated encryption technology as munitions: that is, as a weapon, military technology. If you wanted to export weapons you had to get all sorts of licenses and permission slips, and the government would impose conditions, like don't sell this to our enemies. They brought all sorts of pressure on the author to get him to go through this process or stop distributing his program.
Instead, he printed out the source code of his program and published it, as a book... protected by the First Amendment.
This is exactly the same thing. The files in this case are the source code for a small, mostly (but not entirely) plastic, single-shot handgun.