Yet current federal gun regulation (see above) contains an enormous loophole: While businesses that deal in guns are required to keep records and run background checks, guns can be transferred between private citizens without any record. This makes straw purchases easy. In other words, these laws may generally make guns harder to come by, but those who really want them can still obtain them through private sales.
Also, although it's generally illegal to sell guns across state lines, in practice this is very common. There's abundant evidence that under the current system, guns flow easily between legal and illegal markets. Washington, D.C,. banned all handguns in 1976, and Chicago did the same in 1982. In neither case did the percentage of suicides using firearms -- considered a very good proxy for general gun availability -- fall significantly.
Similarly, Illinois had a background check requirement before 1994, so the local gun market was not affected by the passage of the Brady Act, but gun trace data shows that criminals simply switched from smuggling guns from out of state to buying them illegally in state.
(More: Where 50,000 Guns Recovered in Chicago Came From, New York Times)
How often are guns used in self-defense?
There are no comprehensive records kept of incidents where guns are used in self-defense, so the only way to know is to ask people. Data from the National Crime Victimization Survey suggest that a gun is used in self-defense about 60,000 to 120,000 times each year. Several other surveys confirm this estimate. By comparison, each year about a million violent crimes involve guns. This means guns are used to commit a crime about 10 times as often as they are used for self-defense.
A few surveys in the early 1990s suggested that there are millions gun self-defense incidents each year, but there are very good reasons to believe that these estimates were improperly calculated and these numbers are way off, more than 10 times too high. If the numbers really were this high, this would imply that pretty much every gunshot wound in America is the result of somebody protecting him or herself.
Even among the more accurate surveys, according to a panel of criminal court judges who reviewed survey respondents' stories, about half the time the gun use was "probably illegal," even assuming the gun itself had been purchased legally.
(More: Gun threats and self-defense gun use, Harvard Injury Control Research Center)
Won't criminals kill with other weapons if they don't have guns?
The crux of this question is whether most homicides are planned, or whether killers more often confront their victims with no clear intention. In the second case, adding a gun could result in a fatal shooting that would otherwise have been avoided.
The evidence that weapon does matter goes back decades. In 1968, Franklin Zimring examined cases of knife assaults versus gun assaults in Chicago. The gun attacks were five times more deadly. Moreover, the two sets of attacks were similar in all other dimensions: age, sex, race, whether the victim knew the assailant beforehand, and so forth. A few years later, he repeated his analysis, this time comparing small and large caliber guns. As expected, the victim was much more likely to die from larger caliber guns.