A bit slow to warm up the engines, law enforcement officials in the U.S. and Australia have begun issuing warnings to law enforcement agencies and the public about the dangers of 3D-printing guns. Pro: Video of a printed gun exploding! Con: Their concerns are misplaced.

Fox News obtained a warning issued by the Department of Homeland Security to state and federal enforcement groups.

A May 21 bulletin distributed to numerous state and federal law enforcement agencies and obtained by FoxNews.com states that the guns, which can be made by downloading blueprints into cutting edge computers that mold three-dimensional items from melted plastic, "poses public safety risks" and are likely beyond the current reach of regulators. The guns threaten to render 3D gun control efforts useless if their manufacture becomes more widespread. …

"Limiting access may be impossible," concludes the three-page bulletin.

The memo lists several areas of concern for law enforcement. One is that 3D guns can't be traced, lacking serial numbers or centralized manufacturing. Plastic guns also elude metal detectors, as the Daily Mail demonstrated by bringing a printed weapon on the Eurostar train. Nor can they effectively be subjected to ballistics testing. Such tests rely on the attributes of the weapon that fired a bullet, comparing the firing pin imprint on shell casings and the marks left on a bullet by barrel rifling. In a 3D-printed gun, the barrel and pin can be replaced extremely simply.

Given how difficult these guns are to make, these warnings are mostly as theoretical. Cops in New South Wales are a bit more realistic about their cautions after actually printing a couple copies of the "Liberator," the gun design released by Defense Distributed that was downloaded 100,000 times before the State Department asked that it be removed. The the region's police commissioner did echo the concerns of Homeland Security, but also offered a different warning: these guns aren't safe.

3D guns do not have any of the safety standards, quality control or protection for the user that commercially-produced firearms have.

“The message goes out to anyone with the resources to purchase a 3D printer. Don’t attempt to use a 3D printer to produce a weapon. A 3D-printed gun is not potentially dangerous, it is dangerous,” the Commissioner said.

The video his agency released says more than a thousand words on that subject.

This is actually much more helpful advice. The kind of person most likely to try and build one of these weapons are hobbyists and/or geeky teenagers who want to show off to their friends. If this kind of person gets ahold of a bullet (see below), the prospect of losing a finger or an eye is not insignificant.

But beyond that salient point, the concerns of these law enforcement groups leave out a lot of qualifying considerations.

The first is that any terrorist who plans to use a 3D-printed gun in an act of terror is stupid for reasons beyond the desire to commit an act of terror. As we discovered, 3D-printed guns are difficult to make. They're expensive to make — the "cutting edge computers" Fox News describes are actually printers that cost at least $1,000. That's both far more costly than just going out and buying a low-end gun — and it's the sort of cheap printer that will make the task of printing your "cheap" gun much more difficult.

There's more. The "Liberator" is hard, if not impossible, to aim. It won't propel bullets with as much force as a normal gun. It's extremely slow to reload — if you don't break the barrel firing the first bullet. It's a less effective weapon than a flintlock musket from the Revolutionary War in nearly every respect besides the ability to hide it.

And, finally: to fire the gun, you still need to get a hold of a bullet, as above. And that, you can't exactly print yourself.

None of which is meant to imply that this could someday be a real concern. Someday, we could see very cheap, very effective printers that are commonplace, making the prospect of a society overrun with untraceable, undetectable weapons a real concern. But that day is very much not today.