Building your own firearm is something that's happened on American shores since before this nation was this nation. People have bought parts they couldn't fabricate and built everything else, making their own firearms and then using them. It was never a question.

Then a few years ago, a lawmaker freaked out because it turned out people could still do this. 

It was a hobby supported by a cottage industry that few actually took part in. But when the media started going on and on about the dangers of it, well, criminals started taking notice. That was then used to justify restrictions on these homemade firearms.

And then they were banned in many places.

Following Bruen, I suspect those bans to be short-lived, but Colorado's managed to dodge the proverbial bullet.

A federal judge on Thursday rejected a request from gun rights advocates to block a recent Colorado law prohibiting the possession and transport of certain firearm components not imprinted with a serial number — known as "ghost guns." 

...

In a May 2 order, U.S. District Court Judge Gordon P. Gallagher declined to issue a preliminary injunction, finding the plaintiffs did not have standing to challenge certain aspects of the law. Otherwise, he did not believe SB 279 even implicated the plaintiffs' Second Amendment right to keep and bear arms.

The law "imposes a condition on the commercial sale of a firearm," Gallagher observed. It "does not prevent an individual from buying an unfinished frame or receiver or firearms part kit and in no way infringes upon Plaintiffs’ right to acquire arms. Rather, the Statute requires the purchaser to have the frame or receiver serialized."

Sen. Rhonda Fields, D-Aurora, who was one of SB 279's sponsors, welcomed the decision.

"No one should be able to produce an unregulated, unserialized gun in their home and basement. Our law says you go to a dealer, get a gun, with a background check, it's serialized," she said. "To undermine our process and federal standards gives license to people who want to do harm and do criminal activity with an unregistered gun. We aren't going to tolerate that."

Except that there's no history, text, or tradition of requiring people to get a serial number on a frame or receiver. All things considered, the serial number requirement is a relatively modern invention.

"But ghost guns are a way to avoid a background check!"

It might be for some, but for others, it's a way of having a firearm that doesn't show up on a government form.

See, having to go through a normal gun purchase at a gun store requires that I fill out a Form 4473. That is a de facto version of gun registration, at least until that form hits the magic mark and can destroy it. That just happens to be 20 years, which is also well beyond the point when most small businesses don't go on.

Again, de facto gun registration without calling it gun registration.

Also again, there's no history, text, or tradition from any point in American history other than in the relatively modern period where serial numbers were a thing that was required.

This isn't going to go away. There will most likely be an appeal and then this will move on up the judicial food chain where, hopefully, someone with some damn sense gets hold of it.