She said the only grace in her boy's death was that he "is now with his brother".
McKee also produced a letter that he wished to be read before the court.
"I understand that this is a serious offence, and my actions have changed many lives forever, not just my own, but my victim's family and the community at large," he said.
"I am truly sorry for what I have done and the losses that all have to go through."
He said he has grown significantly while in custody and wishes he could "turn back time" to prevent the tragedy.
"I have taken a son and father, I can never undo that," he said.
His defence lawyer Annabel Ives argued that her terrified client was trying to flee the hostile situation.
High levels of meth were found in Putt's body, explaining his aggression, she said.
As Ives argued for a reduced sentence for her client, Justice Muir interrupted and said she was placing "a very low tariff on human life".
However, during his sentencing remarks, he said McKee's actions could be described as "excessive self-defence" and did not intend to fire a fatal shot, but rather a warning.
The judge said McKee was at a "complete crossroads in his life" as to whether he welcomed his rehabilitation or continued down a criminal path.
McKee and Putt had been on the run from police at the time of the shooting. The gun, described as a dark-coloured pistol wrapped in tape, has never been found.