The last federal assault-weapon ban was passed in 1994 after five school children were killed in 1989 in Stockton, Ca. It expired in 1994. The New York Times says any new ban would have to overcome the opposition of pro-gun lawmakers and the gun lobby. As states and the federal government have experimented with assault weapons bans over the years, gun manufacturers have excelled at finding ways around the restrictions, tweaking their guns just enough to comply with new laws.
The federal ban yielded mixed results. A 2004 federally-funded study by the University of Pennsylvania found that the measure, which included a ban on ammunition magazines that could hold more than 10 rounds, had only a limited impact on gun crime. The study explained that part of the issue was all the exceptions to the law. 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. Another challenge for lawmakers was defining precisely what an assault weapon is, which allowed the industry to continue manufacturing guns similar to those that had been banned. Connecticut has an assault weapons ban similar to the old federal law. Law enforcement officials believe Adam Lanza used legally acquited guns in the Newtown shooting, including a .223 Bushmaster semiautomatic carbine often described as a military-style assault weapon.