Everything You Need To Know About America's Most Popular And Controversial Rifle

The AR-15 is not just America's most popular rifle, it's at the center of the debate on gun control raging through the United States.

As the smoke clears from a shooting at Los Angeles International Airport this morning, there's a familiar rifle laying on the ground by the feet of officers and first responders - an AR-15.

It was also the weapon of choice for James Holmes in Aurora, Colo., and Adam Lanza in Newtown, Conn.

So here are the specs on the most popular, and controversial rifle in America.

It fires a 5.56mm, or .223 caliber bullet. It's a small round that moves very quickly, increasing the weapon's maximum effective range. Despite its small size, the round is tremendously lethal.

The round moves at a rate of nearly 1,000 meters per second.

Magazines for the weapon (that are in circulation in the U.S.) range from 5 to 100 rounds. With proper training, a shooter can effectively and accurately empty a 30 round magazine in less than a minute, maybe faster.

The maximum effective range is between 400 and 600 meters, depending on the barrel length, which varies depending on the model of the rifle.

Much of what makes the AR-15 so popular is its adaptability. Modern AR-15 feature a rail system that allows for custom sights, scopes, and accessories to be placed on the gun.

Very little separates a civilian AR-15 from the M-16s that are the standard-issue rifle for American military rifles. The military versions are semi-automatic, but also come with the ability to fire in a three-round burst, this feature is rarely used.