Arguments about the exact meaning of "assault weapon" obfuscate an important point: When people in the US were allowed to start buying military-style firearms with high-capacity magazines, the number of people killed in gun massacres (defined as shootings in which at least six people die) shot up.
The number of gun massacres and massacre deaths decreased by 37% and 43% respectively after the 1994 ban on assault weapons went into effect, one researcher found. After it expired in 2004, they shot up by 183% and 239%.
There's debate over the effectiveness of this legislation in reducing overall gun crime or firearm deaths, since most gun deaths in the US are suicides and most murders involve a handgun.
But most of the deadliest mass shootings in recent US history have one thing in common: They involved a military-style weapon with a high-capacity magazine.
According to one study, replacing medium- and large-caliber weapons with small-caliber guns would dramatically reduce gun homicide rates.
For a study published in July, researchers examined data about 511 gunshot victims from files kept by the Boston Police Department.
They found that weapon caliber — which refers to the diameter of the firearm barrel and is an indication of the diameter of the bullet — played a big role in how fatal shootings were.
Caliber didn't affect where on the body people got shot. But people who were shot with larger bullets were more likely to die. People shot with medium-caliber weapons (defined as .38, .380, and 9 mm) were more than twice as likely to die as those shot with small-caliber guns (defined as .22, .25, and .32 mm).
People shot with large caliber weapons (.357 magnum, .40, .44 magnum, .45, 10 mm, and 7.62 × 39 mm) were more than four and a half times as likely to die as those shot with small-caliber firearms.
All in all, the researchers found that replacing large- and medium-caliber guns with small ones would have reduced homicide rates by 39.5%.
Reducing access to guns could reduce the number of suicides in the US.
Some gun-rights advocates argue that if you limit access to guns, people will just find other ways to kill themselves or others.
But data indicates that this "substitution hypothesis" is not correct.
More than 60% of gun deaths in the US are suicides, and research has found that people are most likely to try to kill themselves shortly after they decide to do so. People who attempt to do that with a gun as opposed to another method are much more likely to kill themselves.
Data from other countries supports restricting gun access, too. When the Israel Defense Forces stopped letting troops bring weapons home on the weekends, suicide rates dropped by 40%, one study found.
Historically, suicides also dropped after the UK switched from coal-gas ovens — which used a gas that people inhaled to kill themselves — to a different type of fuel. The country saw an increase in the use of other methods to attempt suicide, but it did not offset the drop in suicides by coal gas.