Active shooters with semi-automatic rifles wound and kill twice as many people as those using non-automatic weapons, although chances of dying if hit in either type of assault 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 Parkland High School, Orlando's Pulse night club and Sandy Hook Elementary School.

Semi-automatics, which include some assault weapons, often are thought of as being more lethal. Since they can fire rapidly, 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 all types of guns can be 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 active shooter attacks involving semi-automatic weapons died, the same as those wounded in non-automatic weapon attacks, 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 on types of weapons used in active shooter attacks; FBI figures do not detail whether weapons used were semi-automatic, so the researchers got that information from court and police documents and news media reports.

Semi-automatic rifles cause more deaths and injuries, but "firearms in general, regardless of the type, are extraordinarily lethal weapons," said Dr. Cassandra Crifasi, deputy director of the Johns Hopkins Center for Gun Policy and Research, who was not involved in the research.

A longtime gun owner and sports shooting enthusiast, Crifasi said her understanding of gun culture brings a different perspective to gun research and safety. "The main thing is that there are gun owners like me ... who support commonsense solutions to reducing gun violence," she said.