Hallmarks of Assault Weapons — and What They Do
Bushmaster AR-15

Pictured is one of the guns at the heart of the U.S. assault weapon debate: the Bushmaster AR-15 semi-automatic rifle. See more gun pictures.

© Julie Dermansky/Corbis

When Adam Lanza arrived at Sandy Hook Elementary School on the morning of Dec. 14, 2012, he had four guns in his possession: a Bushmaster AR-15 semi-automatic rifle, two pistols made by Glock and Sig Sauer, and a 12-gauge shotgun made by Izhmash [source: Vance]. He left the shotgun in his car but carried the other three weapons into the school. Ten minutes later, after firing hundreds of rounds, 20 kids and 7 adults, including Lanza himself, lay dead or dying [source: Apuzzo].

Lanza's attack did more than rip the soul from a small town. It triggered vehement arguments about gun control and emboldened President Obama to propose a renewal of the 1994 assault weapons ban, which had expired in 2004. Some of these arguments are filled with misconceptions. Here's one: Assault weapons and assault rifles are the same. They're not. The latter is a firearm developed for military use. The former is a general term meant to bring connotations of ferocity and firepower to certain civilian guns used in nonmilitary situations. Those guns could be rifles, pistols or shotguns, but only if they meet certain legislative criteria.

That brings us back to Lanza. Would the guns he wielded be classified as assault weapons? According to the 1994 ban and the 2013 one proposed by Sen. Dianne Feinstein of California, at least two -- the AR-15 rifle and the shotgun -- would qualify. The two handguns may or may not, depending on the capacity of their magazines.

So, what are the hallmarks, or exclusive features, that earn an ordinary firearm the "assault" label? That's where we're headed in this article.