It’s the weapon of choice for U.S. mass murderers: the AR-15

Editor's note: This story focused on the AR-15 rifle, which was the weapon used in several recent mass shootings. Orlando law enforcement officials initially said this was the same gun type used in the Pulse nightclub shooting, but later clarified that the Orlando shooter was using a Sig Sauer MCX. The Sig Sauer MCX is a rifle with several similarities to the AR 15-style and was originally designed for use by U.S. special operation forces. The NewsHour regrets the confusion.?

GWEN IFILL: The weapon used in the Orlando shootings is at once one of the most popular and most reviled weapons in America, the AR-15, the civilian version of the U.S. military's standard issue rifle.

John Yang has a closer look.

JOHN YANG: The NRA says it's America's most popular rifle, used legally and safely by millions of people. A lawyer for victims' families says it's the gold standard for mass murder of innocent civilians.

The AR-15 has been used in some of the nation's worst mass shootings, at the Sandy Hook Elementary School in Newtown, Connecticut, a movie theater in Aurora, Colorado, an Oregon community college, and now an Orlando gay club.

To learn more about the rifle, its popularity among gun enthusiasts and its place in American culture, we went to a Northern Virginia gun range to speak with former Deputy Assistant Defense Secretary Phillip Carter, himself a gun owner, who knows the AR-15 well from his service as an Army officer.

Why is this weapon so popular?

PHILLIP CARTER, Former Defense Department Official: So, the AR-15 is America's rifle because it's what America's military carries.

It's modeled on the M-16 that's been carried by America's Army and America's Marine Corps and the rest of our services since Vietnam. Today, roughly 20,000 troops carry a similar rifle in Iraq and Afghanistan, and even those who don't serve feel that they're part of that effort when they carry the AR-15.

JOHN YANG: I have read that the recoil is a bit gentler than some other rifles.

PHILIP CARTER: So, the recoil on the M-16 or the AR-15 is designed to be light, so that you can keep it on target and continue to shoot bullet after bullet after bullet. It's by design.

There's a massive spring here in the stock that absorbs quite a bit of the recoil. There's also, by design, a gas system that takes a lot of the gas from the firing of each bullet, and it evaporates it, so that when each bullet is fired, that gas and that recoil isn't coming back on the shoulder each time, but it's actually in the rifle in a more constructive manner.

JOHN YANG: And that feature would also allow a shooter to keep steady.

PHILIP CARTER: It's a military rifle. It's designed to deliver masses of bullets to a very specific target over time. This is a weapon designed to kill in mass quantities. It's a military weapon.

JOHN YANG: So this is essentially a civilian version, you said, of the M-4 or the M-16.

PHILIP CARTER: Yes. This is very much like a civilian version of a Humvee or a civilian version of some other type of military gear. There are some modifications to this that have been made to make it a civilian variant.

What's different on the civilian versions is, it only allows semiautomatic fire. So you flip this to fire, and it allows you to shoot one shot at a time. The military versions would allow you to switch to semiautomatic and then, once more, either for three-round bursts or for fully automatic, if you're shooting an older variant of the M-16.

JOHN YANG: Fully automatic, meaning?

PHILIP CARTER: You squeeze the trigger, and the weapon keeps firing until the magazine runs dry. Your ability to put bullets down-range with this weapon is limited mostly by your ability to reload it.

And the magazine for this rifle looks like this. This is a 30-round magazine that carries 30 bullets of the 5.56-millimeter variety. And it goes into the magazine well right here. It's very easy to reload. It's very easy to get more ammunition in there and continue to shoot at your target.

The ammunition for the M-16 or the AR-15 is a 5.56-millimeter bullet. It's a very small and very fast bullet that does a lot of tissue damage when it hits a person. So just the tip here is the bullet. It's roughly the size of your pinkie tip. But it's propelled forward by a massive cartridge of powder that shoots this at a very high velocity, creating a bullet that can punch through targets, whether they're human or otherwise, with a great deal of lethality and power.

The other thing about this bullet is, because it's so small and moves so fast, it tends to tumble or become volatile when it hits a person, and so it tends to create a very wound and very difficult-to-treat wounds. Again, it's a military weapon. It's not designed for hunting, where you might want to preserve the meat so that you can eat it. It's designed to wound or kill soldiers in combat.

JOHN YANG: There are hundreds of companies in the United States that make verges of the AR-15. The NRA says the weapon can be used not only for hunting, but for sports shooting and self-defense.

For the "PBS NewsHour," I'm John Yang.

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