The amount of such violence seen in modern movies rated PG-13 even exceeded that in films rated R for adults in 2012, said the findings by American and Dutch university researchers in the US journal Pediatrics.
The findings raise concern about the impact that seeing shootings in fictional movie scenes may have on youths in real life, since a large body of research has shown that viewing violent films can increase aggression, the researchers said.
"We do not draw a direct causal link to the recent rise in school and other public shootings but the rise in gun violence in films certainly coincides with those events," said co-author Daniel Romer, director of the Adolescent Communication Institute at the Annenberg Public Policy Center at the University of Pennsylvania.
Researchers found that by analyzing the number of violent sequences in 945 films -- all of them picked from the top 30 films each year from 1950 to 2012 -- that characters were using guns to kill people more often than they had in decades past.
"Gun violence was defined as shooting a gun and hitting a living target," said the study, noting that weaponry such as rocket-propelled grenades and artillery were not counted, nor were hunting scenes.
They found that gun violence has been increasing in all films and more than doubled since 1950.
But violence has spiked specifically in PG-13 movies, a rating that was introduced in 1985.
"Since 2009 it has been as high or higher than R-rated films," said the study.
In 2012, PG-13 movies actually had more gun violence than the average among those rated R for mature audiences.
That meant that the gun violence appeared on average in the top R-rated films in 2012 in about 2.15 five-minute segments per hour. In PG-13 movies, the average rate was about three five-minute segments per hour.
Some of the recent PG-13 movies that were analyzed for the study and "had a lot of gun violence," according to Romer, were The Dark Knight (2008), Terminator Salvation (2009), Inception (2010), Transformers: Dark of the Moon (2011), Captain America: The First Avenger (2011), Mission Impossible: Ghost Protocol (2011), The Avengers (2012), The Amazing Spiderman (2012), and Taken 2 (2012).
"It is interesting to contrast some of the movies that came out earlier and were rated R but that have sequels that are more recently rated PG-13," he told AFP in an email.
"These include the Terminator movies that were rated R in earlier incarnations... as well as the Die Hard series which in a more recent version, Live Free or Die Hard (2007), was rated PG-13."
Recognizing that ample research has already found that exposure to media violence can increase aggression, the research team from Ohio State University, VU (Vrije Universiteit) University Amsterdam in The Netherlands and the University of Pennsylvania decided to do the study to probe whether the presence of gun violence in films for young people could be influencing the spate of mass shootings as a result of the well-known "weapons effect," first established in 1967.
More than 50 scientific studies have since shown that the presence of a weapon can make people act more aggressively, they said.
"It's shocking how gun use has skyrocketed in movies that are often marketed directly at the teen audience," said Brad Bushman, co-author of the study and professor of communication and psychology at Ohio State University.
"It appears sex scenes are more likely to result in an R rating than scenes of violence."
The findings are "troubling," said the study, pointing to the wealth of prior research that has shown violent media can have harmful effects on young people.
"Even if youth do not use guns, the current research suggests that because of the increasing popularity of PG-13 rated films, youth are exposed to considerable gun violence in movie scripts. The mere presence of guns in these films may increase the aggressive behavior of youth," it concluded.
PG-13 movies carry the warning: "Parents strongly cautioned. Some material may be inappropriate for children under 13."