A day before the blueprint for how to 3D print a gun was released to the general public, federal judge Robert Lasnik ordered a temporary freeze on the plans. Judge Lasnik said that the eight attorneys general who filed the suit against Defense Distributed (the company planning to release the gun printing instructions) had established "a likelihood of irreparable harm," according to The New York Times. However, this freeze is only temporary until August 10. So you might want to learn how to call Congress about downloadable guns and protest the release of the blueprints, yourself, if it's something that bothers you.
The 3-D weapons blueprint, if released, will make it easy for any person to print a variety of guns, from a style of handgun to a type of AR-15. What's more, the person who downloads the gun at home won't have to register it anywhere since it will technically be "home made." That means that it will become infinitely more difficult for the government to keep track of the number of weapons currently at large in the United States, as well as to ensure that people with criminal or mental health records don't have immediate access to a firearm.
If you want to tell your representatives that you'd like to ensure every gun owner is required to register their firearms and go through background checks prior to owning one, then you can first find out who your representative is by using the search page for the House of Representatives. Then you can tell that representative that you're not comfortable with the idea of people being able to print out guns in their living room without telling anyone.
If you want to call your senator, too, then you can call the U.S Capitol Switchboard at (202) 224-3121, which will connect you to the office of your Senator (it's always an option to write mail to your senators, too, but since this is such a time-restrictive matter you should probably call.)
If you want to know how to contact all of your representatives in the House and in the Senate, you can use the Call My Congress site which will give you the information for all of your congressional reps.
If you're feeling nervous about talking to someone on the phone, you can look at a mock script staged by EveryTown. Though it doesn't directly address the specific request to ban the release of any online instructions for printing 3-D guns, you can easily tailor the speech so that it does:
"Hi, my name is [name], and I'm calling from [city, state]. I don't need a response. I'm calling to urge [rep name] to oppose the release of Defense Distributed's online instructions for 3-D weapon printing to the general public. I feel strongly that the time has come to put the safety of all Americans first. We should not make it easy for people to print their own guns at home, without undergoing a background check or having to register their weapon at any point. Thank you!"
EveryTown also provided two pointers for leaving these messages: make sure to do it even if you get sent to voicemail, because your message will still be tallied, and be sure to stay polite with anyone you speak with along the way, regardless of who they are or what they believe in.
Currently Democratic lawmakers like Senate Minority Leader Chuck Schumer (D-NY) are speaking out against the potential availability of homemade guns. "The danger that could happen can be enormous,” he said at a press conference earlier in July. “To have crazy people have easy access, to have terrorists have easy access to this kind of website and allow them to make plastic AR 15s undetected — so-called ghost guns — justifies the imagination.”
Even Donald Trump has gone out of his way to say that he'd already spoken to the NRA about the matter, and the idea of printing guns didn't "make much sense" to him. Though it's unlikely for a law explicitly banning the creation of homemade weapons to be passed (since there's already a law in place banning this very act), your communication to your representatives could work to trigger a much bigger act of momentum.
If Congress were to collectively stand against the release of those gun printing instructions, it could not only prevent the instructions from being released, but perhaps even further clarify what types of gun restrictions are necessary in this nation, such as universal background checks and assault weapons bans.