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Will Senate Democrats be able to end debate on their new gun control bill Tuesday night? President Obama says that it is “not right” to continue the debate. But he might be more afraid that Senators will point out all of his false claims and reveal the gun control bill’s dangers.

Mr. Obama got it all backwards in his April 3rd speech in Colorado: "tougher background checks . . . won’t infringe on the rights of responsible gun owners, but will help keep guns out of the hands of dangerous people."

The president kept claiming this week and last week that: “as many as 40 percent of all gun purchases take place without a background check” and that "background checks have kept more than 2 million dangerous people from buying a gun.” But both statistics are false.

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Start with the 40 percent figure. That number comes from a very small study covering purchases during 1991 to 1994. Not only is that two decades-old data, but it covered sales before the federal Brady Act took effect on February 28, 1994. The act required federally licensed dealers to perform background checks.

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And what's more, Mr. Obama conveniently forgets that the researchers gave this number (well, actually 36%, not his rounding up to 40%) for all transfers, not just for guns sold. Most significantly, the vast majority of these transfers involved within-family inheritances and gifts.

Counting only guns that were sold gives a very different perspective, with only 14 percent not actually going through federally licensed dealers. But even that is much too high as there were biases in the survey. For example, two-thirds of federally licensed dealers at the time were so-called “kitchen table” dealers who sold gun out of their homes and most buyers surveyed were likely unaware these individuals were indeed licensed.

By the way, that survey also found that all gun-show sales went through federally licensed dealers. If President Obama really trusts the study, he should stop raging about the “gun show loophole.”

The truth is, the databases the government uses to determine eligibility for gun purchases are rife with errors.

This is the same problem experienced with the “No Fly” list. Remember the five times that the late Sen. Ted Kennedy was “initially denied” flights because his name was on the anti-terror “no fly” list? His name was just too similar to someone that we really did want to keep from flying. By Obama’s method of counting, that means the “no fly” list stopped five flights by terrorists.

For gun purchases, the Bureau of Alcohol, Tobacco, Firearms and Explosives dropped over 94 percent of “initial denials” after just the first preliminary review. The annual National Instant Criminal Background Check System report explains that these cases were dropped either because the additional information showed that the wrong people had been stopped or because the covered offenses were so many decades old that the government decided not to prosecute. At least a fifth of the remaining 6 percent were still false positives.

All these denials mean delays for many law-abiding gun buyers. Although this is merely an inconvenience for most, initial denials cause dangerous delays for people who suddenly, legitimately need a gun for self-defense, such as a woman being stalked by an ex-boyfriend or spouse.

Beyond the crashes in the computers doing the checks and the initial denials, another 6 percent of checks fail to be completed within two hours, with most delays winding up taking three days.

President Obama ignores what happens to those who suddenly feel threatened. A gun really can make a huge difference in being able to defend against assailants.

Indeed, my own research suggests these delays from the background check system likely increase violent crime, even if ever so slightly. Perhaps not too surprisingly, rape appears to be the crime most sensitive to these delays.

Furthermore, there is no real scientific evidence among criminologists and economists that background checks actually reduce crime. In fact, a 2004 National Academy of Sciences panel concluded that the Brady background checks didn't reduce any type of violent crime. Nor have other later studies found a beneficial effect.

The number of criminals stopped by the checks is also quite small. In 2010, there were over 76,000 initial denials, but only 44 of those were deemed worthy for prosecution and only 13 individuals were convicted. Even those 13 cases don’t tend to be the “dangerous” criminals Obama claims are being stopped.

The delays have other consequences. States that have applied background checks to sales by private individuals have seen around a 20 percent drop in the number of gun shows, eliminating for many poorer people a relatively inexpensive source of buying guns. For gun shows, which usually only last two days, even a three-day delay means that no sale will be made.

The fees in the Senate bill on those getting background checks on gun transfers are not trivial, ranging from $35 to $50 in most states and rising as high as $125 in the District of Columbia.

This effective tax will price poor blacks -- the people most likely to be victims of violent crime -- out of being able to buy a gun for self-defense. Americans might also not be ready for a national registry.

Expanded background checks might intuitively seem to make sense. But how laws work in theory is often different from how they work in the real world. Unless the databases somehow are dramatically improved, expanded background checks are likely to do more harm than good.