Gun laws are mandated by state-level governments; therefore, they vary state-to-state. State gun laws include regulations on purchasing firearms, concealed carry permits, and ammunition. A magazine is an ammunition storage and feeding device attached to a repeating firearm. Magazines come in various shapes and sizes and can be either removable or integral to the firearm.
Large-capacity magazines, also known as high-capacity magazines, are typically magazines with a high number of rounds of ammunition and are usually associated with semi-automatic assault weapons or machine guns. Large-capacity magazines typically have ten or more rounds of ammunition, although this number is arbitrary and not universally agreed upon. The term "high capacity magazine" is a minority term, in the sense that a minority of states consider anything over 10 rounds to be "high capacity."
Large-capacity magazines enable a shooter to fire repeatedly without taking the time to reload, increasing the shooter's ability to injure and kill large numbers of people in a short amount of time. Large-capacity magazines have been used in most of the ten of the deadliest U.S. mass shootings in the last ten years. For example, the Las Vegas shooter in 2017 was able to shoot 90 rounds within ten seconds without having to reload. He was using an assault rifle with a bump stock and large-capacity magazine. The shooter killed 50 people and injured hundreds.
In 1994, Congress adopted the Violent Crime Control and Law Enforcement Act, which banned the manufacture, transfer, and possession of semi-automatic weapons and made it unlawful to transfer or possess large-capacity ammunition feeding devices. This act expired in 2004 but did work to reduce the use of large-capacity magazines in crime down to 10%. This number climbed back to 22% by 2010.
The federal ban on large-capacity magazines has ended. However, nine states and the District of Columbia have enacted laws banning large-capacity magazines. These states are California, Colorado, Connecticut, District of Columbia, Hawaii, Maryland, Massachusetts, New Jersey, New York, and Vermont.
Each of these nine states has its own specific regulations regarding capacity limit, prohibited acts of large-capacity magazines, and the treatment of pre-owned large-capacity magazines. For example, in Colorado, the legal magazine capacity is 15 rounds. It is illegal to sell, transfer, or possess large-capacity magazines, and pre-owned large-capacity magazines are grandfathered (allowed). Some states and the District of Columbia do not allow pre-owned large-capacity magazines to be grandfathered. Large-capacity magazines that were owned before the law was put in place are still illegal.