A Criminal Court jury on Tuesday found Myles Stout guilty of reckless homicide and reckless endangerment in the slaying of 18-year-old Myles Compton.
The state had sought a verdict of second-degree murder, which would have carried a prison sentence of 15-25 years.
The incident occurred March 9, 2011, in the upstairs bedroom of the home of Kevin Driscoll, where Stout was living at the time.
Stout had told detectives that he did not know the handgun was loaded when he put it to the chest of Mr. Compton and pulled the trigger.
There was testimony at the trial that two handguns in the bedroom had both been cleared prior to the shooting, and there was no proof on how the gun got loaded.
Stout and Mr. Compton were acquaintances who had gone on a number of outings together.
There was no testimony of any animosity between them at the time of the shooting.
The jury deliberated about three hours.
Sentencing by Judge Barry Steelman will be Nov. 5.