Correction: An earlier version of this story incorrectly identified one of the weapons involved in Sunday’s shooting in Orlando as an AR-15. Orlando Police officials first classified the weapon used in the rampage as an “AR-15-type assault rifle.” On Monday, officials said the weapon used was a Sig Sauer MCX. While in many ways similar to the AR-15 family of rifles, the MCX relies on a different gas system to operate and cannot be fairly classified as an AR-15. Both weapons can fire the same type of ammunition at roughly the same speeds and share a similar history.

Assault rifles similar to the one used in the deadly mass shooting in Orlando on Sunday have lately become the weapon of choice for gunmen intent on harming the maximum number of people in a minimum amount of time.

Gun-rights advocates have fiercely resisted any calls for tighter regulation of these weapons in response to mass shootings, particularly AR-15 assault rifles. The NRA estimates there are around 5 million AR-15 rifles in circulation, with hundreds of thousands more manufactured each year. They point out that the vast majority of the weapons are never used to commit a crime.

The heated discussions over gun control and gun rights that inevitably follow mass shootings like the one in Orlando typically revolve around interpretations of the U.S. Constitution's Second Amendment. In full, the amendment reads, rather murkily, "A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed." The wording leaves plenty of room for legal and political wrangling over the meaning of words like "well regulated," "militia," "right," "people," "keep," "bear" and "arms."

The National Rifle Association has explicitly embraced a message of Second Amendment "absolutism" in recent years. "Absolutes do exist," NRA President Wayne LaPierre said after the December 2012 massacre at Sandy Hook Elementary School. "We are as ‘absolutist’ as the Founding Fathers and framers of the Constitution. And we’re proud of it!"

For LaPierre, this absolutism means opposition to universal background checks and national gun registries. It also means a wide latitude in allowing gun owners the choice of weapons to defend themselves. "We believe in our right to defend ourselves and our families with semiautomatic firearms technology,” LaPierre said.

Here's what you need to know about the guns some are calling "the gold standard for mass murder," after Orlando shooter Omar Mateen used the assault-style rifle Sig Sauer MCX to kill at least 49 people. (Editor's note: This video has been updated with more specific information.) (Gillian Brockell/The Washington Post)

Of course, semiautomatic firearms technology didn't exist in any meaningful sense in the era of the founding fathers. They had something much different in mind when they drafted the Second Amendment. The typical firearms of the day were muskets and flintlock pistols. They could hold a single round at a time, and a skilled shooter could hope to get off three or possibly four rounds in a minute of firing. By all accounts they were not particularly accurate either.


Compare those specifications with the capabilities of a modern-day AR-15. According to the makers of one model of the gun, a good shooter can effectively fire 45 rounds per minute. The guns are stable and accurate at distances five to 10 times farther than a typical Second Amendment-era gun. Standard magazines can hold 30 rounds, and shooters can swap out magazines and continue firing in just a matter of seconds.

In short, guns today are capable of inflicting far more carnage than anything the framers could have imagined. That's a point that's driven home with chilling effectiveness by this brief video by States United to Prevent Gun Violence.

In itself, that isn't an argument for banning everything other than muskets. Technology evolves. It makes no more sense to say an AR-15 isn't protected by the Second Amendment than it does to say that computers or ballpoint pens aren't protected by the First.

But evolving technology does call for evolving regulation. And, in practice, the implementation of the Second Amendment has never been strictly "absolute." Most gun owners accept that civilians typically can't own fully automatic rifles or tanks or nuclear weapons. Our understanding of the "arms" of the Second Amendment has evolved over the years, subject to shifts in political and legal norms.

In recent years, at least, public perception of what the Second Amendment permits has changed. In December of last year, for the first time, a majority of Americans opposed a nationwide ban on the sale of assault weapons according to ABC/Washington Post polling.

That poll was taken in the immediate aftermath of the San Bernardino shootings, in which two shooters used semiautomatic AR-15-style rifles to murder 14 people. Two months later, a man walked into a plant in Hesston, Kan., armed with an AK-47, killing three people and injuring 14 more. A few months later, another individual walked into an Orlando club armed with an assault rifle similar to an AR-15, killed 49 people and injuring dozens more.

As the NRA says, the overwhelming majority of semiautomatic assault-style rifles are never used in crime. But they make it exceedingly easy for the criminally inclined to kill and wound dozens of people.

More from Wonkblog:

We've had a massive decline in gun violence in the United States. Here's why.

Guns are now killing as many people as cars in the U.S.

White resentment is fueling opposition to gun control, researchers say