On an episode of Meet the Press that aired Sunday, December 16th, two days after the Newtown shooting, Senator Dianne Feinstein announced that she would bring a new assault weapons ban to the floor in 2013. Feinstein was one of the authors of the 1994 assault weapons ban, which expired in 2004.

The rationale behind such a ban would be to reduce access to the types of gúns that would make it easy for one person to kill many people quickly. The 1994 ban placed restrictions on firearms that had certain characteristics of military weapons—for example, rifles with bayonet lugs, flash suppressors and pistol grips. Some gun enthusiasts derided the 1994 ban as a “cosmetic ban” because it prohibited certain guns that looked dangerous, while allowing other, equally deadly weapons to remain legal.

Whether you support Senator Feinstein’s bill or not, it’s important to understand what she proposes to ban, and it would be easier to assess the relevance of such a ban if the bill logically differentiated among weapons based on their capacity to kill. Most Americans know enough about guns to have formulated at least a vague opinion about what should and shouldn’t be legal. Through popular television programs, movies and video games, even people who have never fired a gun have developed some notion about the difference between, say, an M-16 and a snub-nosed revolver. But there are a huge variety of guns sold on the civilian market in the U.S., many of which are not well understood by the general public. This overview, while not comprehensive, is designed to clarify the significant differences between various types of firearms, with an emphasis on the weapon’s potential to kill many people quickly.

Much of the recent debate about which guns to ban has emphasized differences between handguns and rifles. That distinction is more complex than it might seem. We think of handguns as smaller weapons that shoot smaller bullets1. But some pistols have the same caliber, rate of fire and capacity as military rifles. At close range, specialized handguns can be as effective as rifles, either when used for hunting or when used to inflict mass casualties. In 2007, Seung-Hui Cho shot 49 people (32 fatally) at Virginia Tech, armed only with handguns.

A semiautomatic handgun with a high-capacity magazine. Photo © Matt Valentine

A semiautomatic handgun with a high-capacity magazine. Photo © Matt Valentine

Rather than focus on the size of the gun, I’d like to highlight two more relevant factors that make some guns more lethal in mass shooting scenarios than others, which are A) rate of fire and B) capacity. Any gun can be deadly, but all other things being equal, a gun that can fire rapidly for a sustained period without needing to be reloaded clearly has the potential to kill more people than a gun that can only be operated with frequent pauses. More »