The Brady Campaign offers what seems like a pretty reasonable definition of assault weapons (“Federal Gun Laws: Assault-Style Weapons: Frequently Asked Questions.”)
 In response to those who claim that the 1994 Assault Weapons Ban didn’t work, I would just point out, first, that the ban contained numerous loopholes that greatly hindered it. “Assault weapons and large-capacity magazines manufactured before 1994 were exempted from the ban, meaning that more than 1.5 million assault weapons remained in circulation. In addition, the country’s stock of large-capacity magazines actually continued to grow after the ban, because it remained legal to import them as long as they had been made before the ban.” The law also inadequately spelled out what constituted an assault weapon, allowing “the industry to continue manufacturing guns similar to those that had been banned.” Second, a 2004 study financed by the Justice Department concluded that the ban did lead to a small reduction in gun crime (Michael Luo and Michael Cooper, “Lessons in Politics and Fine Print in Assault Weapons Ban of ’90s,” New York Times, December 19, 2012).
 As proof that assault weapons can have defensive purposes, some have pointed out that during the LA Riots some Korean store owners used semi-automatic rifles to defend their grocery stores. Three points here. First, it’s not clear that assault weapons were used. In the following news clip, for instance, one individual (presumably a store owner or friend) can be seen with a more traditional hunting rifle and another with a handgun: “Korean store owners defend their businesses during the 1992 LA riots.” Second, it seems clear that assault weapons were not needed for defense. Evidently just displaying traditional rifles and handguns and firing them into the air was enough to deter looters (Ashley Dunn, “Looters, Mercants Put Koreatown Under the Gun: Violence: Lacking confidence in the police, employees and others armed themselves to protect mini-mall,” Los Angeles Times, May 2, 1992). Third, even if assault weapons were in fact needed to keep back looters, it doesn’t follow that the benefits of allowing such weapons to remain legal outweigh the costs. As recent events have made clear, assault weapons allow deranged gunmen to murder large numbers of individuals in a relatively short period of time. Making it harder for would-be killers to acquire such weapons would most certainly save lives, and achieving this goal makes a ban worthwhile, even if every few decades or so such a weapon might be used to keep a group of looters at bay.
 Michael Bloomberg, “6 ways to stop gun madness,” USA Today, December 19, 2012. See also Demand A Plan to End Gun Violence.