Before last week's massacre in Las Vegas, most Americans probably had never heard of bump stocks, which police say Stephen Paddock used to increase his rate of fire while shooting at country music fans from the 32nd floor of the Mandalay Bay Resort and Casino. Since then the accessories have become so notorious that YouTube is taking down videos showing them in action and gun owners are rushing to buy them in anticipation of a ban, a step that President Trump and Republican legislators say they are willing to consider. Even the National Rifle Association has said new restrictions on bump stocks may be appropriate.

Although there is less to the NRA's concession than meets the eye, it shows the organization is squishier on gun rights than its reputation suggests. It also illustrates the strength of the urge to do something (or be seen as doing something) in response to mass shootings, even when that thing is unlikely to have any measurable impact on the frequency or deadliness of such crimes.

"Despite the fact that the Obama administration approved the sale of bump fire stocks on at least two occasions," the NRA said last Thursday, "the National Rifle Association is calling on the Bureau of Alcohol, Tobacco, Firearms and Explosives [ATF] to immediately review whether these devices comply with federal law. The NRA believes that devices designed to allow semi-automatic rifles to function like fully automatic rifles should be subject to additional regulations."

The NRA was referring to letters the ATF sent to manufacturers of bump stocks certifying the legality of their products. "The stock has no automatically functioning mechanical parts or springs and performs no automatic mechanical function when installed," the agency informed the Moran, Texas, company Slide Fire Solutions in 2010. "Accordingly, we find that the 'bump-stock' is a firearm part and is not regulated as a firearm under Gun Control Act or the National Firearms Act." The ATF sent a similar letter to a competing manufacturer, Bump Fire Systems (also based in Moran), two years later.

The ATF determined that a firearm equipped with a bump stock, which harnesses recoil energy to help the shooter fire repeatedly without having to flex his trigger finger, does not qualify as a "machinegun" under the National Firearms Act because it still fires just once "by a single function of the trigger." The agency also concluded that the bump stock itself does not meet the definition of a regulatable "firearm" under the Gun Control Act. Since these conclusions seem like straightforward applications of the statutory language, it is quite unlikely that the ATF would change its position after taking the second look urged by the NRA.

That means a ban on bump stocks would require new legislation, which the NRA opposes. "It's illegal to convert a semiautomatic to a fully automatic," NRA Executive Vice President Wayne LaPierre said on Face the Nation yesterday. "We think ATF ought to do its job, look at this, and draw a bright line." But the ATF already looked at this, and it determined that bump stocks do not "convert a semiautomatic to a fully automatic," which fires "more than one shot…by a single function of the trigger." That is the "bright line" drawn by the law that Congress passed, and the ATF is merely enforcing it.

LaPierre said the NRA won't support legislation to ban bump stocks because it worries that any such bill would turn into "some Christmas tree on the Hill," festooned with new restrictions long sought by gun controllers such as Sen. Dianne Feinstein (D-Calif.). That prospect is not far-fetched, although the more ambitious the bill becomes, the less likely Republicans and conservative Democrats are to support it. But in practice, the NRA's opposition to new legislation means it does not really favor "additional regulations" for bump stocks, which cannot be imposed through administrative action without bending the law for blatantly political reasons.

It is nevertheless significant that the NRA saw fit to go through the motions of throwing gun owners who like bump stocks (or might like to try them) under the bus. By contrast, Gun Owners of America (GOA)—which advertises itself with a quote from former Texas congressman and Republican presidential candidate Ron Paul, who called it "the only no-compromise gun lobby in Washington"—firmly opposes a ban on bump stocks. "Any type of ban will be ignored by criminals and only serve to disarm honest citizens," says GOA Executive Director Erich Pratt, who adds that it's "sad to see some Republicans quickly call for a vote on gun control."

Pratt describes bump stocks as accessories that "help gun owners with disabilities fire their weapons." It is true that people whose ability to pull a trigger is limited by arthritis or other conditions might find bump stocks useful. But Slide Fire describes its products as "fun, exciting and entertaining," and that is the way online enthusiasts (such as the ones YouTube has decided to censor) present the devices. Presumably the NRA calculated that it was not politically smart to defend fun against the demands of activists and politicians who portray bump stocks as an intolerable threat to public safety.

That portrayal is questionable, since noncriminal motives account for approximately 100 percent of the demand for bump stocks, which as far as I know have never been used in a mass shooting before. Previous mass shooters nevertheless have managed to kill dozens of people. The previous record, in the attack on the Pulse nightclub in Orlando last year, was 49, compared to 58 in Las Vegas. Bump stocks, which trade accuracy for speed, may have enabled Paddock to injure more people than he otherwise would have, but it's not clear that they increased the death toll, since he might have killed a similar number of people (or even more) by firing more slowly and carefully.

The ratio of nonfatal to fatal gunshot wounds in Las Vegas was much higher than usual in mass shootings. The most recent count of nonfatal injuries is 489, and most were caused by gunfire. That means at least four people (and probably more) were injured by gunfire for each person killed. By comparison, the ratio for the nine next deadliest mass shootings in recent U.S. history (including the 1966 attack at the University of Texas in Austin, which also involved a shooter firing from a high structure) was less than 2 to 1 in almost every case. The one exception was the 2009 attack at Fort Hood, where the ratio was less than 3 to 1.

Still, if legislators assign zero weight to the interests of gun owners who use bump stocks for legal recreational purposes, the possibility that future mass shooters might use them is enough to justify a ban. Furthermore, such a policy is likely to pass muster with the federal courts, given the way the Supreme Court has interpreted the Second Amendment (as covering guns "in common use for lawful purposes" but allowing bans on "dangerous and unusual weapons"). In this context, the only people apt to oppose a ban on bump stocks are gun owners who use them or can imagine using them, fussy libertarians (like me) who argue that a tiny minority's potential misuse of a product does not justify prohibiting it, and gun rights supporters who worry about the opportunity that legislation aimed at bump stocks presents or the precedent it sets.

By raising the possibility of new restrictions on bump stocks but opposing them in practice, the NRA is trying to split the difference on this issue, creating the appearance of a concession without actually making one. Still, its position probably increases the likelihood of a legislative ban, since "even the NRA" seems to agree that bump stocks pose a danger the government needs to address.

It could be worse. In the wake of the 2012 Sandy Hook massacre, LaPierre demanded "an active national database of the mentally ill" to prevent anyone qualifying for a psychiatric diagnosis (nearly half the population, at one time or another) from buying a gun.