> because you still can't get the other parts that aren't printed

Every part except the firing pin is now printable (you can print quite strong carbon-fiber reinforced parts at home). The firing pin can be made from a nail or similar piece of metal.

> You can't get bullets

Bullets are mostly easy enough to make. One of my neighbors growing up was a competitive shooter who competed nationally and internationally. He manufactured his own ammo in his home shop, using tools any boomer dad had access to, like a lathe, presses and very accurate scales. He didn't really pay any more for ammo than we did per round. The only reason criminals don't do it is because buying factory ammo on the gray and black market is so easy.

The most difficult part to make would probably be the primers, but that still isn't difficult for any chemist.

Here's a (old) video of someone in Europe making their own ammo at home: https://www.youtube.com/watch?v=J5Cx4idIIe0

In my country, Guns and Bullets are heavily controlled(Even airsoft is banned here). You can not get explosive unless you prove you have legit use for it(usually for mining). And of course DIY gun or bullet is no-no and you will be jailed.

Even in police force or army, they literally count every single bullet, and for every fired bullet, it must be explained in detail.

Maybe that's why we have low gun-related crime here.