The rifle used in the Texas elementary school shooting is known as a "DDM4 Rifle." It's modeled after the M4 carbine, the U.S. military's go-to rifle, according to a blog post by the gun's maker, Daniel Defense.

The Daniel Defense rifle can be classified as an AR-15 type. A key difference between the Daniel Defense rifle and the M4 carbine is that the military's version can switch to fully automatic or fire a three-round burst depending on the model.

AR-15-type rifles can be purchased for as little as $400, but the Daniel Defense rifle is on the high end of around $2,000 or more. These rifles can also be financed, with customers paying less than $100 a month.

The Daniel Defense rifle is not sold with sights. According to pictures of the shooter's guns posted on Instagram, he appears to have purchased a battery-powered holographic sight that typically sells for around $725.

A sniper's scope uses magnification to aid in hitting targets from a great distance. Holographic sights are designed to speed up the process of short-range shooting by helping to fix on targets more quickly.

The man who killed 19 children and two teachers bought his guns legally days before the attack and soon after his 18th birthday, a law enforcement briefing said.

He bought one AR-style rifle from a federally-licensed gun dealer in the Uvalde area on May 17, according to a state police briefing given to Sen. John Whitmire. The next day, he bought 375 rounds of ammunition, and bought a second rifle on May 20.

Officers recovered one of the rifles from Salvador Ramos' truck and the other was found in the school, according to the briefing.

It says Ramos dropped a backpack with several magazines full of ammunition near the school entrance, and that he was wearing a body-armor style vest but that it had no hardened plates inside.

On Wednesday, President Joe Biden said that "the Second Amendment is not absolute" as he called for new limitations on guns in the wake of this week's massacre at a Texas elementary school.

When the amendment was approved, he said, "You couldn't own a cannon. You couldn't own certain kinds of weapons. There's always been limitations."

Biden was speaking at the White House before signing an executive order on policing on the second anniversary of George Floyd's death.

He that he would visit Texas with first lady Jill Biden in the coming days to "hopefully bring some little comfort to the community."

"As a nation, I think we must all be there for them," he said. "And we must ask, when it god's name will we do what's needed to be done.

And the State Department says the school shooting and other mass casualty incidents are hurting America's standing abroad and giving comfort to U.S. rivals and adversaries.

Spokesman Ned Price said Wednesday incidents like these not only cause damage to the U.S. global reputation but also upset and confuse friends and allies who don't understand how they can continue to happen.

"The fact is that what happens in this country is magnified on the world stage," Price told reporters a day after a gunman killed 19 children and two adults in the Texas school shooting. "And countries around the world, people around the world, are going to fixate on what transpires here — oftentimes out of envy, but again that's when we're at our best."

Price said the shootings "will have implications for our standing" and the U.S. diplomats posted around the world are "very mindful of that."

He said that despite the State Department's foreign policy focus, the shootings hit American diplomats as "a real punch to the gut."

Meanwhile, schools around the country increased security as a precaution.

In Connecticut, where the 2012 Sandy Hook Elementary School shooting killed 20 first-graders and six educators, state police said they were sending extra troopers to schools Wednesday, although no specific threats had been received.

"This assault on the most innocent of our citizens is deeply disturbing and heartbreaking," Connecticut state police Col. Stavros Mellekas said in a statement. "At this time, our focus will be on protecting all school populations here in our state."

Schools in Washington, D.C., Atlanta, Virginia, Maryland and Florida also were among those increasing security and offering counseling.

And actor Matthew McConaughey, who was born in Uvalde, called on Americans to act now to control an "epidemic" of mass shootings.

"Once again, we have tragically proven that we are failing to be responsible for the rights our freedoms grant us," McConaughey posted on his Instagram account. "We cannot exhale once again, make excuses, and accept these tragic realities as the status quo."

The actor doesn't describe any specific laws or policies he wants adopted. He doesn't mention gun control.

"As Americans, Texans, mothers and fathers, it's time we re-evaluate," he wrote. "We have to rearrange our values and find a common ground."

"This is an epidemic we can control, and whichever side of the aisle we may stand on, we all know we can do better."