In 1991, after George Hennard shot 22 people to death at a Luby's cafeteria in Killeen, Texas, Sarah Brady said the mass murder showed the need for a federal ban on "assault weapons." Brady, the head of Handgun Control Inc., wrote an op-ed piece in which she asked, "Is it going to take a massacre in every congressional district for enough members to find the backbone to put public safety ahead of the profits of the assault weapon lobby?"

It was an odd connection to make, since the pistols Hennard used, a Glock 17 and a Ruger P89, were not covered by the legislation Brady was demanding. A decade later, she and her organization, now called the Brady Campaign to Prevent Gun Violence, are still trying to pass off non sequiturs as common sense.

In a recent press release, Brady says the string of sniper murders that have shocked and unnerved people in Maryland and Northern Virginia demonstrate the wisdom of the "assault weapon" ban, which Congress passed in 1994. Noting that the law is set to expire in two years, she warns, "We do not want to put more military-style weapons capable of such devastation—and worse—back on our streets."

There's an obvious problem with arguing that an existing law is needed to prevent crimes like the sniper attacks when it has manifestly failed to do so. But the weakness in Brady's reasoning goes deeper than that.

First of all, Brady misleads the public by stating that the sniper may be using an "assault rifle," which is a gun designed for soldiers that can be switched from semiautomatic (firing once per trigger pull) to automatic (firing continuously). The legislation Brady wants renewed has nothing to do with automatic weapons, a.k.a. machine guns, which have been strictly controlled by the federal government since the 1930s.

Brady and her allies try to obscure this point by fostering confusion between actual military weapons (such as assault rifles) and guns that bear a cosmetic resemblance to them. The guns covered by the "assault weapon" ban were singled out based primarily on their scary looks rather than their capabilities.

Even if that were not the case, the law would be irrelevant to the sniper murders, every one of which has involved a single shot fired from a distance. Depending upon the shooter's skill, any rifle is "capable of such devastation."

Hence Brady's logic suggests that what we really need is a ban on rifles. And we already know how she feels about handguns.

If the "assault weapon" angle on the sniper murders is counterintuitive (to put it kindly), Brady's other recommendation—a national "ballistic fingerprint" system—seems more plausible. The idea has enough superficial appeal that the Bush a dministration, after initially expressing skepticism, has agreed to study it.

Under this scheme, manufacturers would test-fire every new gun and supply the government with the bullet and shell casing, the markings from which would be entered into a database. If the gun were ever used in a crime, police could match a bullet or shell casing found at the scene to the weapon's serial number and original purchaser.

The weaknesses in such a system are manifold. Matching ballistic markings is an uncertain art with no objective threshold for verifying that two bullets came from the same gun. As with ordinary fingerprints, the judgment of an examiner may be especially iffy when only fragments are recovered or when he knows what the result is supposed to be.

Compounding this problem, a gun's "fingerprint" changes with use, and it can be deliberately altered by switching parts or scraping the inside of the barrel. Criminals who don't know how to doctor their weapons can simply use one of the 200 million or so guns already in circulation. And even if they use a gun whose signature is on file, they can escape detection if they steal it or buy it from a source other than a gun store, which is what they usually do anyway.

Supporters of a national gun database concede these points but argue that it still might help to solve some crimes. The only downside, they say, is that such a system would upset gun owners, who see it as firearm registration in disguise, a prelude to confiscation.

Ballistic fingerprint enthusiasts dismiss this concern as groundless—which shows they have not been listening very closely to people like Sarah Brady.