CHICAGO — Gunmen with semi-automatic rifles wound and kill twice as many people as those using non-automatic weapons, although the chances of dying if shot with either type of weapon are the same, a new analysis shows.

Researchers examined FBI data on nearly 250 "active shooter" incidents in the United States since 2000. Almost 900 people were wounded and 718 were killed.

One in four of these attacks involved semi-automatic rifles. These weapons automatically load each bullet after firing, although firing requires pulling the trigger for each round.

Recent attacks involving semi-automatics include the shootings at Marjory Stoneman Douglas High School in Parkland, Florida; the Pulse nightclub in Orlando, Florida; and Sandy Hook Elementary School in Newtown, Connecticut.

Semi-automatics, which include some assault weapons, are often thought to be more lethal. Since they can fire rapidly, the chances of being hit in those circumstances are high, the study shows.

But in "active shooter" attacks, which tend to occur in confined spaces and with an intent to kill, the results suggest that all types of guns are equally deadly, said lead researcher Dr. Adil Haider, a trauma surgeon at Brigham and Women's Hospital in Boston.

Overall, 44 percent of people hit in such attacks involving semi-automatic weapons died, the same as those wounded in attacks with non-automatic weapons, showing that "the death rate if you got hit by a bullet was the same," Haider said.

"Active shooters are hell-bent on killing people," he said. "The big difference — and this is not such a big surprise — is if you give them a semi-automatic, they're able to shoot twice the number of people."

The average number of people wounded in semi-automatic attacks totaled nearly six, versus about three in attacks with a non-automatic weapon. Roughly four people were killed on average in semi-automatic attacks, compared with about two in other attacks, the study found.

The results were published Tuesday in the Journal of the American Medical Association.

Haider said the study highlights a need to better track details about the types of weapons used in such attacks; FBI data does not specify the weapons used, so the researchers got that information from court and police documents and news media reports.