What are the chances of jail time vs. just probation for accidentally shooting someone in PA, victim alive and well

A friend of mine accidentally shot his girlfriend while trying to unload a jammed round in his pistol. The slide slipped as he pulled it back and discharged the weapon as his girlfriend unknowingly entered the doorway at the same time the round went off. The bullet entered her side and exited her lower back, missing all vital organs and was released from the hospital a few days later. She is alive and well. Based off of this info, what are the chances of him going to jail vs. just getting probation? He's being charged with felony gun charges, gross negligence, assault. I'm not sure exactly his charges.