They actually are open source, and there is indeed a lot of material out there to help people with everything they need to build their own. The only part that is illegal to make on your own is the part with a serial number on it, for tracking purposes.
The only part that is illegal to make on your own is the part with a serial number on it, for tracking purposes.
Perhaps that is the case elsewhere, but to point out that in the US, it is legal on the Federal level to make your own complete firearm for personal use. Assuming no state specific laws prohibit it, it is by default legal. ATF FAQ page. If you are not an FFL holder, and are not going to sell the firearm it does not need any serial number. All NFA restrictions still apply to homemade firearms.
The practice of legally homemaking firearms pre-dates 3D printing, with 80% AR-15 lowers being a modern and widespread example.
Technically, you're supposed to give it a serial number and register it with a local FFL. Giving it a serial number (or NOT giving it a serial number) on your own would run afoul of many new 'ghost gun' laws that have been put in place. This is obviously, dependent on location. At the US-federal level, so long as you don't plan on selling it I don't think it is required.
This may be true for some specific US states, but declaring it wholesale true in the US is wrong. From the ATF FAQ on homemade firearms:
You do not have to add a serial number or register the [privately manufactured firearm] if you are not engaged in the business of making firearms for livelihood or profit.
If you weren't jumping on your replies like some addicted meth head, you'd notice that I added some additional clarification about 20 seconds after I initially posted. But I guess 20 seconds is too much for people to wait before they check their inbox.
Wrong again. I've provided a source with links to all applicable legislation on the subject matter on a per-state basis. These rules do exist in some jurisdictions.
It's kind of wild to realize that some states are trying to outlaw owning blocks of steel that have zero machining operations on them because benchtop CNC exists. I don't even know how they think that this is going to work; make every single machine and tool and die shop have an FFL in order to own a Bridgeport?
This is a fundamental problem with gun control; the tools that are used to make firearms--and to make ammunition components--are widely available, and have many uses outside of making firearms. Most people don't make their own guns because it's more expensive if that's all you're doing, unless that's your business.
I think what you and the other commenter are having friction with is that on your first comment declaring that it is "technically required" you did not specify that it was state by state, and the vagueness gave the impression it was a statement applying nationwide.
Now you are showing a link talking about state-by-state legislation, which is a more restricted and nuanced reframing of the original statement. Beyond that, your link seems to show 39 states do allow homemade firearms with no additional state laws, making that the majority. While declaring the rules one way or the other for the whole nation would be incorrect, saying that they are allowed is less incorrect since the majority of states do allow them.