The Associated Press and the USA TODAY Network combined forces to investigate accidental shootings involving children, researching more than 1,000 incidents over a 2½-year span. In all, those shootings claimed the lives of more than 320 minors and more than 30 adults.

The investigation used information collected by the Gun Violence Archive, a nonpartisan research group, news reports and public sources. It analyzed the circumstances of every death and injury from accidental shootings involving children ages 17 and younger from Jan. 1, 2014, to June 30 of this year — more than 1,000 incidents in all.

Among the findings:

— Fatal accidental shootings occur more often than the federal government tracks. In 2014, the last year for which statistics were available, the U.S. Centers for Disease Control and Prevention counted 74 unintentional firearms deaths of children. The AP and USA Today Network found 113 such deaths the same year, suggesting the federal government missed a third of the cases.

— Deaths and injuries spike for children under age 5, with 3-year-olds the most common shooters and victims among young children. Nearly 90 3-year-olds were killed or injured in the shootings, the vast majority of which were self-inflicted.

— Accidental shootings spike again at ages 15-17, when victims are most often fatally shot by other children but typically survive self-inflicted gunshots.

— The shootings most often happen at the children's homes with handguns legally owned by adults for self-protection; hunting accidents are far less common.

— The shootings are more likely to occur on weekends or around holidays such as Christmas.

— As a region, the Deep South has rates of accidental shootings involving minors far above the national rate. Louisiana, Tennessee, Alabama, Mississippi and Georgia are among the top 10 states with the highest rates.