“That punk pulled a Glock 7 on me,” reported heroic law-enforcement officer John McClane. “It’s a porcelain gun made in Germany. It doesn’t show up on your airport metal detectors and probably costs more than what you make in a month.”

A note for the gun-control gang: “Die Hard 2” wasn’t a documentary.

The 1990 action flick was only one episode in the story — the mostly fictitious story — of plastic phantom pistols that can be walked through airports by terrorists and other nogoodniks. Spy novels of the 1970s and 1980s told of the KGB-invented “Troika” pistol, which sometimes made its way into media stories and government reports in spite of the fact that nobody ever seems to have actually seen one. There’s also the plastic stealth pistol sneaked into a courtroom by a mafioso in “The Dark Knight” for the purpose of knocking off the crusading district attorney.

Bad news for Gotham: Batman isn’t real.

Neither are high-tech phantom polymer guns — and all the angst and wailing about 3D printers churning out plastic gats from sea to shining sea doesn’t change that.

Urban legends are a poor basis for making public policy.

The federal government has undertaken two significant initiatives on the matter of undetectable plastic guns: banning them on the one hand, and then trying to invent them on the other. In the 1980s, the Pentagon invested in what turned out to be a fruitless project to build nonmetal firearms using ceramics. At the same time, Ronald Reagan signed into law a ban on the possession of firearms that can pass unseen through metal detectors.

That’s government work for you: banning something that doesn’t exist while spending great heaping piles of money trying to invent the thing you want to ban, and failing.

The unhappy truth is that you don’t need a space-age plastic gun to sneak past airport security. A 2015 test found a 95 percent failure rate among TSA agents trying to identify guns and other contraband. By 2017, ABC News reports, the TSA failure rate was down to around 80 percent.

You won’t find any news stories about high-tech plastic weapons being used in the real world to hijack airplanes or assassinate charismatic DAs in court, because — to repeat — they do not, at the moment, exist. Not in the way the anti-gun crowd imagines. The “Liberator” pistol at the center of the current panic is basically a plastic tube with a place for a bullet to sit. You could carve one out of wood.

Approximately 0.0 percent of the homicides committed annually in New York City involve a 3D printed gun

You know what does exist? Machinists, and for generations they have had the skills and tools to build firearms, and many of them have. Americans have been building their own guns since some forgotten frontier smith invented the Kentucky long rifle far from any factory or federal regulator.

Question: When’s the last time you heard about somebody knocking over a 7-Eleven or shooting up a school with a homemade gun?

We have an odd tendency to focus on the exotic when it comes to gun violence in the United States. There isn’t any evidence of undetectable homemade guns being used in violent crime in the United States. It just doesn’t happen. In the same way, politicians and television producers love the charismatic rat-a-rat of a machine gun but, here in the real world, legally owned fully automatic weapons have been used in — count ’em — two homicides since 1934, when the government started keeping score. Both were in Ohio, and one of the perpetrators was a police officer using a department-issued firearm.

So, what is going on with the 3D printers?

They have been around for a while now, and people have been making all sorts of interesting things with them, from implants to help repair shattered bones to chemical molecules. And some have made guns with them. That is perfectly legal, so long as the guns in question are not otherwise prohibited — i.e., fully automatic weapons or those built to slip past metal detectors.

The Obama administration had attempted, under the flimsiest of pretexts, to suppress the online publication of plans for building such weapons by classifying them as munitions subject to export controls. We’ve been down that road before: In the 1990s, the Clinton administration tried the same thing with an encryption tool called Pretty Good Privacy, insisting that anybody who sent a copy to a friend in Canada was an illegal international arms dealer. It was bull, and everybody knew it. The government eventually relented, and now ordinary Canadians and Belgians have access to strong encryption — which doesn’t seem to have mattered very much.

Approximately 0.0 percent of the homicides committed annually in New York City involve a 3D printed gun. Approximately 90 percent of them involve somebody with a prior police record, including many offenders previously charged with violent crimes and illegal firearms possession — a problem about which the powers that be are doing approximately squat. It’s worse in Chicago and Los Angeles.

We have real problems. Why focus on the imaginary ones?