While much remains unknown about the specific weapons Stephen Paddock fired from the 32nd floor of the Mandalay Bay Resort and Casino in Las Vegas, killing at least 59 people and injuring potentially hundreds more, authorities said Monday night that 23 firearms were recovered in the hotel room.
The sound of gunfire captured on videos recorded during the massacre indicates that Paddock used at least one automatic weapon, a type of firearm that is highly regulated in the United States though a fairly common find at gun shows and firing ranges, including one near Las Vegas that allows customers to shoot military-grade weapons.
It was unclear how Paddock would have acquired an automatic weapon, if he did use one. Those weapons can be legally owned if made before May 1986 and registered with the federal government, or owned by licensed dealers.
So far, at least one has been identified as an AK-47 type rifle, outfitted with a stand to steady it and improve accuracy, said people close to the ongoing probe. Lombardo said the weapons that have been recovered range in caliber from .223, which is associated with AR-15 style rifles, and .308, which is a caliber commonly used in hunting rifles. Lombardo was unsure if any of the weapons were automatic. Scopes were also recovered on the scene, and at least one firearm was a handgun.
Agents with Alcohol, Tobacco and Firearms have yet to determine if Paddock modified mechanical components to a semiautomatic rifle to make it fully automatic, Lombardo said, which would be illegal. He also could have used a legal modification like an attachable crank to simulate automatic fire, which depresses the trigger faster than a finger and can be bought online for as little as $40.
It is important to note the distinction between a semiautomatic rifle and a fully automatic weapon. Semiautomatic rifles such as the AR-15 patterned rifle — owned by millions of Americans and found on the scene after mass killings at San Bernardino, Calif.; Aurora, Colo., and Newtown, Conn. — are the civilian variant of the military’s M-16 and M-4 rifles.
One squeeze of the trigger means one round leaves the barrel, which physically limits the amount of fire to how quickly the operator can pull the trigger. AR-15 pattern rifles typically take 30-round magazines, which feeds ammunition into the weapon using a tension spring.
Some states, such as California, regulate the size of magazines, but Nevada does not. A trained shooter can easily remove one magazine from the weapon, load another from a tactical vest or pocket, and continue firing within seconds. There are higher-capacity magazines available, but they are prone to malfunctions and misfeeds.
An automatic weapon, by contrast, fires continuously as long as pressure is applied to the trigger and ammunition is available. While semiautomatic weapons are often incorrectly referred to as “machine guns,” an automatic weapon’s originally designed mechanical system — used to feed, eject and ready the next round — is what makes it a machine gun.
Semiautomatic weapons can also legally simulate automatic fire with “bump” modifications to the stock that reduces recoil and lets the shooter hold the weapon in a way that allows rapid fire, according to the Trace, a nonprofit website that examines gun violence in the United States.
Paddock’s choice of a firing position 400 yards from the stage at a high overlook suggests a plan of attack to fire into a densely packed area where accuracy would not be a top concern. That distance is near the 500-yard effective range for an M-4, but machine guns typically have longer barrels which extend range. A weapon such as the M-249 Squad Automatic Weapon, or SAW, is effective at 800 meters for individual targets.
The difference between the two is enormous from a lethality standpoint. On the battlefield, for instance, an M-4 rifle is a semiautomatic rifle. Training manuals suggest 12 to 15 rounds a minute for sustained firing, which would avert the risk of its barrel overheating.
The SAW fires the same 5.56mm caliber ammunition, the military equivalent to .223, with metal links attached to the rounds. Manuals suggest 100 rounds for sustained fire, though 200 rounds can be used in dangerous combat situations.
A typical scenario in Iraq and Afghanistan would involve a SAW gunner firing an entire starter belt of 100 linked rounds at the beginning of a firefight to quickly suppress the enemy. It would take only a few seconds to fire the belt.
The high number of firearms found at the hotel suggest a concern for overheating rifle barrels. The barrels can reach several hundred degrees, turning orange and even blue as rounds travel thousands of feet per second through them.
Automatic weapons such as the SAW and the larger M-240 have lever releases on the barrel, allowing one to be swapped for another using a oven-mitt-like glove.
The National Rifle Association says Nevada law allows the purchase of machine guns and silencers in compliance with federal law and regulations.
Devlin Barrett contributed to this report.