Police were called to the family's home in Henry County at 2:41 a.m. Saturday and found the younger boy had shot his older brother, the Atlanta Journal-Constitution reported.
The brothers, along with a friend who was sleeping over at the house, found their mother's gun at some point in the night, "which at the time had been unloaded," said Henry County police Sgt. Joey Smith.
"During the course of the evening and early morning hours, one of the boys had evidently loaded the weapon," Smith said. "The 14-year-old at some point pointed the weapon at his brother and pulled the trigger, which resulted in the 15-year-old being struck in the chest area."
Smith said that while the shooting has been ruled accidental, "the facts will be presented to the district attorney's office for possible prosecution on both the juvenile and the mother."
Names of those involved have not been released.