When a liberal friend asked me the other day if I didn’t “at least” support a ban on assault weapons, I had to ask: what is an assault weapon?

My speaker was momentarily flummoxed—he gamely attempted a comeback: an assault weapon, he said, is defined as “the kind of weapon that was used at Newtown.” I said he’d have to do better than that.

It’s hard to tell which is more in evidence in the current gun debate over guns—the emotion, which is understandable after the horror of Newtown, or the ignorance, which is unpardonable in those seeking to change policy.

John Lott has a piece in the Wall Street Journal this morning on the mislabeling of weapons and misunderstanding of the effects of the Federal Assault Weapons ban. Senator Diane Feinstein was author of the 1994 assault weapons ban that gun control advocates wish to revive.

Feinstein cites studies by o studies by Chris Koper and Jeff Roth, both criminology professors, for the National Institute of Justice to support her claim that the ban produced results. She claims that in their first study, Koper and Roth found that the ban reduced “total gun murders.” Perhaps Lott read the study more carefully than Feinstein:

In fact, [Kofer and Roth] wrote: "the evidence is not strong enough for us to conclude that there was any meaningful effect (i.e., that the effect was different from zero)."

Messrs. Koper and Roth suggested that after the ban had been in effect for more years it might be possible to find a benefit. Seven years later, in 2004, they published a follow-up study for the National Institute of Justice with fellow criminologist Dan Woods that concluded, "we cannot clearly credit the ban with any of the nation's recent drop in gun violence. And, indeed, there has been no discernible reduction in the lethality and injuriousness of gun violence."

There is also the question of defining guns:

Moreover, none of the weapons banned under the 1994 legislation or the updated version are "military" weapons. The killer in Newtown used a Bushmaster .223. This weapon bears a cosmetic resemblance to the M-16, which has been used by the U.S. military since the Vietnam War. The call has frequently been made that there is "no reason" for such "military-style weapons" to be available to civilians.

Yes, the Bushmaster and the AK-47 are "military-style weapons." But the key word is "style"—they are similar to military guns in their cosmetics, not in the way they operate. The guns covered by the original were not the fully automatic machine guns used by the military, but semiautomatic versions of those guns.

The civilian version of the Bushmaster uses essentially the same sorts of bullets as small game-hunting rifles, fires at the same rapidity (one bullet per pull of the trigger), and does the same damage. The civilian version of the AK-47 is similar, though it fires a much larger bullet—.30 inches in diameter, as opposed to the .223 inch rounds used by the Bushmaster. No self-respecting military in the world would use the civilian version of these guns.

A common question is: "Why do people need a semiautomatic Bushmaster to go out and kill deer?" The answer is simple: It is a hunting rifle. It has just been made to look like a military weapon.

But guns aren’t just for hunting tasty animals. Ask Sarah McKinley about that. Mrs. McKinley’s husband died of cancer during the 2011 Christmas season. On New Year’s Day, when two men tried to break into her house, the eighteen-year-old mother protected her infant and herself with a 12-gauge shotgun. McKinley killed one of the intruders and the other ran.

Sometimes, however, the law-abiding citizen is forced to engage in a more protracted struggle than Ms. McKinley’s. A single-shot rifle that requires reloading is not going to be much use against multiple attackers, Lott points out. Magazines are ridiculously easy to make and, in the case of a ban, the criminal element won’t be deterred one bit.

Ms. Feinstein is also proposing gun registration, which sounds like a good idea. Lott says that such registration doesn’t work, and indeed Canada recently dumped its registry rules for that reason.

But back to my conversation with my liberal friend. Just to tweak him, I said—provocatively—“What if George III had taken away all our guns?”

“Who?” he said.

That is what we are up against.