3DPrinting

You clearly didn't read anything I said after that first line but this is just too fun:

A CNC can make a gun from start to finish that you wouldn’t be worried about blowing your fingers off when you pulled the trigger, without adding outside hardware to.

Mostly tells me you have no idea what is inside of a firearm outside of "magic".

Over simplifying, but modern firearms generally consist of

1. A frame: This is usually a mix of plastic and metal for comfort, weight, and heat dissipation reasons. But there is nothing saying you can't have an all metal frame. Some parts will receive load, some parts are purely cosmetic/ergonomic. This is demonstrably not a problem for either 3d printer or mill.
2. Lots of pins and levers: These are the mechanisms that actually make the gun go bang when you pull the trigger. And, depending on how spicy you want to get, continue to go bang while you hold down the trigger. Again, some parts are stressed, some aren't. There are ways to do all plastic that should last at least a few hundred rounds. The issue is more one of tolerances. Getting a 3d printer to be able to print with that level of precision is more work than people want to put in. Similarly, getting a mill capable of that level of precision is also a mother (Adam Savage of Will Smith's Tested fame has a lot of videos where he is basically tackling this challenge for different projects). But also? These are the parts that "wear out" and are completely uncontrolled and can be bought online trivially. So why manufacture this yourself in the first place?
3. Springs. Good fricking luck milling your own springs with the required properties. Also good fricking luck printing your own springs. That said, I actually watched a REALLY cool video where someone proof of concept made a gun out of 3d printable leaf springs and while the guy doing it was a complete and utter dipshit, it was a work of engineering beauty that you couldn't pay me enough to hold in my hand... But, again, these are trivially easy to buy online so why bother?
4. The last major part in this oversimplified breakdown is the barrel (and how you seal it but I am just going to include that here). These are the parts that experience the most forces and heat when the gun is fired since that is the part where the bang happens. Everything else you can probably get away with some cheap mild steel. That? You need some good stuff otherwise you are going to learn just how weak that cheap stock was. You CAN mill chrome moly and the like but that is a much bigger challenge than cutting through cheap steel like it is butter and amplifies all of the above tolerance issues. I will outright say that you can't print this in plastic even though I have seen in person demonstrations of proof of concepts of that.

And the cheap steel problem? Go look up pictures of the "custom" guns used in conflicts like The Troubles. A lot have cracked or split barrels and the like because of that exact issue.

Which, like I said in the comment you refused to read, is why you just buy the hard parts online or in cash at your local gun store (... might need to go to a specialty shop instead of a Walmart). Because they are not controlled since they generally need to get replaced eventually anyway.

At which point? Mills and Printers both work great. It is just that the former needs a lot more machinist skill to be done. Whereas the latter is just downloading an STL.

Just because this topic really intrigues the engineer in me:

Even if you are REALLY anti-gun (moreso in the sense of absolutely zero meaningful gun control laws that don't predominantly target minorities and lower income folk) but can still appreciate an engineering problem:

Vice, back before it was a shithole content farm that talks about how right wing chuds are sticking it to the man, had a REALLY good video where a reporter went to a gathering of 3d printed firearms enthusiasts and even printed their own gun with the help of one of them. There are a lot of uncomfortable parts that kind of felt like fallon tussling the dipshit's hair back in the day, but it is also one of the very few (easily reached on youtube) videos that show what 3d printing a gun actually is.

inRange TV has a video that doesn't get too into the making of a 3d printed gun but does show some of the recent advances (and I believe one of the models shown is quite similar to a certain mario brother's favorite toy...) which is useful from the perspective of how 3d printed parts are coupled to off the shelf parts and so forth.

And while the owner of the channel is a real dipshit and it is explicitly NOT about 3d printed guns (because that would hurt his monetization), Forgotten Weapons did a sponsored video where he turned a common handgun into basically a PDW using a kit. And, in the process of doing that, it really highlights what part of a firearm is the legal and controlled part and what parts can be easily replaced... or purchased in a discount bin. And Forgotten Weapons, in general, is really good at actually disassembling/field stripping firearms to show the inner workings and the engineering. And it is a fun thought process to think through what processes were used to make those parts and what processes could be used to make those parts instead.