Joseph V. Loughrey, 44, told police he had been trying to sell the guns Saturday at Twigs Reloading Den in East Lackawannock Township, 60 miles north of Pittsburgh.
He unloaded the magazine at home, but didn't realize a bullet was still in the chamber, Lt. Eric Hermick said. His son, Craig Allen Loughrey, was shot in the chest and died at the scene.
State police Lt. Eric Hermick said Sunday the father had secured a rifle in the back of the truck and placed his pistol on the console when the handgun went off. Hermick said police are reviewing surveillance video from the store, which helped lay out the chain of events; the video is not being released.
"It is very clear-cut exactly what transpired here," Hermick said of what he called clearly an accident. "As he's laying it down, it discharges."
An autopsy was scheduled for Sunday and the results of the investigation will be given to Mercer County District Attorney Robert G. Kochems, Hermick said. A message left with Kochems was not immediately returned Sunday.
Hermick said the father was very distraught and cooperative; he said he doubts there will be charges, but that it's up to the district attorney. The father could face charges, including involuntary manslaughter, Hermick said.
"It's obviously negligent and reckless to some degree," he said. "It's obviously in that gray area, where it's a true accident. But is there negligence or recklessness with him not clearing the chamber?"
A message left at a telephone listing in the father's name was not returned.