Ahmad Al Aliwi Alissa bought the gun six days before the shootings in which 10 people were killed according to his affidavit on the arrest warrant. The weapon had been modified with an armrest, according to a law enforcement source. The Ruger AR-556 is a type of AR-15, the military rifle that existed used in many other mass shootings. The pistol version is essentially the same weapon as the rifle, but with a shorter 10.5-inch barrel and an adjustable stabilizing strut on the back – held against the shoulder – “to aid accuracy, balance and recoil management” Ruger website.

“The AR-15 platform weapon – whether in a long gun or a pistol – has essentially the same firepower. It is semi-automatic for combat,” said Timothy D. Lytton, an expert on the weapons industry at Georgia State University.

“The AR-15 pistol is almost something of a novelty. Essentially, it’s the same gun, but with a much shorter barrel and barrel, and it’s a smaller gun. Just like some people might want to drive a sports car because they do that Like the sense of compactness and speed, they essentially take a combat weapon or a combat style weapon and shrink everything down to some sort of miniature version. “

“You can put that thing under a jacket”

The AR-15 was developed for the US military in the 1950s. It was invented by Eugene Stoner who worked for a company called Armalite, which is where the AR comes from. The number 556 refers to the caliber – 5.56 millimeters.

“So the shorter barrel and stock make for a smaller weapon that is easier to carry with you,” Lytton said. “It would certainly make it more concealed. You can tuck this thing under a jacket in such a way that it would be difficult to tuck an AR15 platform rifle under your jacket.”

AR-15s are usually semi-automatic, which means that a bullet is fired every time the trigger is pulled. They are loaded with magazines that automatically feed bullets when the weapon is fired.

The magazine capacity varies and usually starts at 10 rounds – the legal limit in some states – but sometimes also at 30 rounds.

In 2018, the city of Boulder, Colorado passed a ban on the sale and possession of assault weapons and large capacity magazines. Earlier this month A district court judge prevented the city from enforcing its ban.

AR-15-style rifles have been used in some of the deadliest mass murders in recent US history, including a 2012 filming in an Aurora, Colorado movie theater that killed 12 people.

An AR-15 rifle was also the weapon a former student used to butcher 17 people at Marjory Stoneman Douglas High School in Parkland, Florida. Parkland shooting is one of the shootings listed in Boulder’s Ordinance Banning Assault Weapons.

“It’s not your normal gun”

Colorado state law doesn’t include the type of firearms Boulder attempted to ban – semi-automatic rifles that can accommodate a detachable magazine and have a pistol grip, folding or telescopic stock, or any device that allows the gun to be attached to the Non-stabilizer can be stabilized hand trigger – under the list of illegal or dangerous weapons.

The state bans magazines that can hold more than 15 rounds, while Boulder’s Regulation prohibits magazines that can hold more than 10 rounds.

“They know enthusiasts like it because, as they like to say, it’s some kind of fire-breathing weapon on the line,” Lytton said of the AR-15 pistol.

“It’s not your normal pistol. It has the firepower of a long gun. And also because it’s classified as a handgun in some states. It wouldn’t have restrictions on long guns with a short barrel … There’s a certain amount of debate about it. as is the status of the gun, but one could imagine that it could qualify as a pistol and as a pistol it is not subject to sawed-off shotgun regulations. You cannot take a regular AR-15 in many states and just saw the muzzle off and with a hideable one long gun running around. This allows you to basically just have a shorter muzzle and do the same thing. “

AR-15 and similar military rifles like AK-47 are often referred to as assault rifles or assault rifles, although members of the arms industry prefer to refer to them as modern sporting rifles or MSRs.

These weapons were restricted by federal law for 10 years until the so-called assault weapons ban expired in 2004. This ban restricted certain components of the weapon, such as pistol grips and bayonet locks, and limited the magazine capacity to 10.

Gun lovers are fans of the AR-15

The versatility of the AR-15, including lightning suppressors, pistol grips, and even bayonets, makes it popular with gun aficionados.

“If you want to build a rifle, take an AR-15 frame and put a long barrel filter on it,” said Daniel G. O’Kelly, director of the Dallas-based International Firearm Specialist Academy and former agent at the Bureau for Alcohol, tobacco, firearms and explosives.

“If you want to build an AR-15 pistol, just put a pistol grip and short barrel on it. Because of these characteristics, it is classified as a pistol instead of a rifle under federal definitions.”

O’Kelly said there of hundreds of AR-15 manufacturers in the US. It is the most popular rifle in the country.

“It’s modular and can be customized to suit your needs or tastes,” he said.

“All functions are to click into place, to snap off. So you can change the caliber, barrel length, type of handle, type of shoulder rests, type of locations … I don’t know if I could name a toy – it would probably sound silly – but there are Toys out there that were probably popular with kids because of all the accessories you can get to modify or fit in and make yours like no other. That’s a big part of the appeal. “

CNN’s Whitney Wild, Veronica Stracqualursi and Aaron Smith contributed to this report.