The DefCAD Liberator design (since improved on) actually works for many dozens of rounds until stress cracks start showing up on the weapon, indicating you need to stop using it. The one that blew up in testing was using a 5.7x28mm PDW round instead of the .380ACP the thing was designed to handle. It does not explode without ample warning with .380. And after all, you only need a round or two to ‘upgrade’ to a ‘real’ arm.
Yes, you can make a zip gun out of home improvement supplies. But if you do that, there’s invariably video records of you buying the pieces, if not computer records from your electronic transaction these days. And no, paying cash will still not stop the video records (which are indexed to purchase times now!) So if you have to abandon it after using it, there’s a pretty good chance they will be coming to look for you. This is what has these people scared: With a 3D printer there is *NO* record they can try to track back.
I am confused as to how this is even possible. The projectile used in a .380ACP cartridge is 9mm in diameter; the projectile used in a 5.7x28mm is 5.7mm in diameter. The overall length of a .380ACP cartridge is 25mm; the overall length of 5.7x28mm cartridge is 40.5mm. These cartridges are not physically compatible in any way that I can conceive. I think that your source gave you inaccurate information.
So if you have to abandon it after using it, there’s a pretty good chance they will be coming to look for you. This is what has these people scared: With a 3D printer there is *NO* record they can try to track back.
I would suggest that if you have motive and the authorities were to find a gun printed on a 3D Printer at the scene of a crime and then found that you possessed a 3D Printer that prosecutors would have a fairly easy time convincing a jury of your peers that you were the perpetrator. This would be especially true if the authorities found plans for making a gun in your computer and remnants of the same type of filament the gun was produced from were found in or on you or your friend's printer.
My knowledge of the “Liberator design” is confined to just a few articles. I do however reload 9mm Luger, 9mm Makarov, and .380ACP brass. Although the .380ACP takes less powder than the others, there is certainly enough powder contained in the case to cause serious injury, blindness or even death if there was a failure.
I have been on many forums where we spent hours debating the relative safety of manufactured firearms that were designed and tested to be reliable weapons for both the military and the public. Although I appreciate that you are speaking in SHTF theoretical terms as to why you think that guns made completely out of plastic on an inexpensive home printer are an important development... I am sure that you would agree that in practical terms that at this time it would be both foolish and dangerous to actually try and use or depend on this type of weapon.
I believe that the link that I provided showed a lower receiver for an AR-15 type of rifle which was printed. I do not know enough to say whether or not this is a good and safe application. I believe the same group that produced the Liberator design has also gone this direction. At least in this design the firing chamber, barrel and other parts that come into contact with projectiles and high pressure gasses appear to be made from appropriate materials.
It seems likely that the “Liberator” was designed as a proof of concept device and not intended at this stage to be actually used or depended on. Whereas for literally hundreds of years designs have been available for easily manufactured homemade guns made from commonly available materials which were actually designed for practical purposes.
I don't mean to make uninformed assumptions about your background here. If you are helping to develop this type of thing... I applaud your efforts. If however you are new to firearms and are planning on printing one of these things with the intention of actually using it... I would strongly suggest that you first go the more traditional route of getting instruction with a manufactured firearm and master that first. Then immerse yourself in the finer details such as the study of ballistics so that you can make an informed decision as to whether a homemade or printed firearm actually has any safe and practical purpose for your needs.