Deleon Alonso Smith, 19, died from a gunshot wound to the throat on Tuesday.
Police in Houston said Mr Smith found the gun and was taking pictures of himself holding the weapon when it fired.
His cousin, who had also been taking photos with the gun, was in another room in the apartment when the accident occurred.
Mr Smith's uncle, Eric Douglas, told KHOU-TV: "I went up there and tried to revive him, but there was no reviving him, he was dead."
Relatives told KPRC-TV Mr Smith had two small children and was starting college on Wednesday.
"It's a numb feeling. It's still unbelievable," his grandmother Alma Douglas told the news station.
Sky News
Police are investigating the shooting as an accident
