Three mass shootings that killed 34 people over the past week involved semi-automatic weapons and magazines capable of holding dozens of bullets — all of which were legal to purchase by the shooters.

In Dayton, Ohio, police said Sunday afternoon the shooter legally purchased his .223-caliber weapon online and then had it transferred to a local arms dealer. Police said he affixed the rifle with a 100-round drum magazine and was carrying 250 rounds with him.

He may also have skirted federal law prohibiting short barrels by using a "pistol brace" affixed to a pistol that fires the .223 bullet usually used in rifles.

Dayton shooter used a gun that may have exploited an ATF loophole

In El Paso, Texas, it's believed the shooter used an AK-47 variant to kill 22 people. In Gilroy, California, last week, the shooter used a similar gun based on the AK, the Soviet-developed rifle replicated worldwide.

Ohio and Texas allow the guns and the magazines to be sold. California bans the sale of magazines that hold more than 10 rounds, but the Gilroy shooter legally bought his gun in Nevada.

Most rifles that fire the .223-caliber round are in the "AR-style," or variants of the ArmaLite AR-15 that has been produced in recent years for sports shooters and home protection.

Those rifles usually come with 30 or fewer rounds in a magazine. But increasingly gun manufacturers have catered to shooters looking to have 40, 60 or 100-round magazines that traditionally were shunned because they were heavy and cumbersome.

High-capacity magazines have been around for decades, but cheaper, lighter material has led to more firing consistency. A new generation of shooters have created a market for the once-novelty devices, said Rick Vasquez, a former ATF program manager that runs Active Crisis Consulting.

"You still don't really see them used much in the military for lack of consistency and all the added weight," Vasquez said.

High-capacity magazines have been used in other mass shootings, including in Las Vegas, Sutherland Springs, Texas, and Parkland, Florida.

Vasquez said the Trump administration's recent move to limit access to bump stock devices hinged on changing a legal definition. Magazine size bans need legislation, he said, like the federal ban that ran from 1994 to 2004.

"States can regulate this pretty quickly, but I don't see Texas or Ohio taking that up anytime soon," Vasquez said.

'A normal individual seeing that type of weapon might be alarmed'

In El Paso, the shooting suspect is believed to have posted an online manifesto referencing a weapon similar to the AK-variant semi-automatic rifle seen in surveillance video from the Walmart in Texas.

The rambling online missive references the Wassenaar Arrangement Semi-automatic Rifles, or WASR-10, a Romanian AK-variant imported by some American distributors. One company, Florida-based Century Arms, calls itself "North America's Premier AK manufacturer." Representatives from the company did not respond to messages from USA TODAY.

This is the same type of weapon used by the shooter at the garlic festival in northern California last week.

El Paso's police chief also noted that it was not only legal for the shooter to purchase the firearm, but Texas allows open carry of rifles in public places.

“A normal individual seeing that type of weapon might be alarmed, but technically it was in the realm of the law,” Chief Greg Allen said.

'It’s not going to stop the mass shooting, but it can lower the amount of casualties'

High-capacity magazines are banned in nine states - including California, Hawaii and New York - and Washington, D.C. Most of the states define high-capacity magazines as being able to hold 10 rounds of ammunition or more.

Michael Siegel, a professor at the school of public health in Boston University, conducted an analysis that shows states with high-capacity bans are less likely to experience a mass shooting.

Siegel said he believes efforts to curb mass shootings would be more effective if they focused on banning magazines instead of military-style weapons.

“It’s not going to stop the mass shooting, but it can lower the amount of casualties when you have an event like this,” he said.

Siegel said that even if there was a ban on assault weapons, a person can still commit a mass shooting with a non-military-style firearm because the gun could have a high-capacity magazine.

“If you have a pistol but you have a 30-round magazine on that pistol, you can still do a lot of damage in a short time,” he said.

The Federal Assault Weapons Ban of 1994 in effect until 2004 included a provision that banned high-capacity magazines that held more than 10 rounds of ammunition.