The mother of a NSW woman stabbed to death by her teenage son has described his 13-year jail sentence as "a joke", saying her grandson should never be allowed to walk the streets again.
Bradley Craig Mottram, now 22, "snapped" at a home in Inverell, in northern NSW, in October 2015 when his 51-year-old mother Simone said something that upset him, the NSW Supreme Court heard on Thursday.
Acting Justice Peter Hidden handed the "troubled young man" an 18-year sentence with a non-parole period of 13-and-a-half years, saying it was clear he was in a disturbed state of mind and was remorseful.
"That wasn't a sentence, that was a joke," Ms Mottram's mother Maureen O'Bryan told AAP outside court.
"That guy should not be out on the street with what he did ... it's a joke."
The court heard Mottram punched his mother before beating her with a bourbon bottle and going to the kitchen to grab a carving knife.
He then stabbed his mother repeatedly in the chest, abdomen, neck and face before placing the weapon on her body and covering her with a blanket.
Mottram fled the scene in her car and wrote admissions in a notebook under an entry titled "My Last Words".
"Holy s***, I'm sorry, this was not planned," he wrote.
"I didn't mean to, she just wouldn't shut up."
He accused his mother of "wiring" him from birth.
The court heard Mottram had a "troubled" upbringing and was diagnosed with borderline personality disorder.
His mother, who also suffered mental health issues, was a drinker and Mottram was exposed to short-term partners and domestic violence.
By 2015, as a 19-year-old, he was abusing cannabis and codeine and was experimenting with hallucinogens.
The court heard Mottram made various comments about falling out with "bad people" who were out to get him, including outlaw bikie gangs.
After the murder, Mottram described his mother as "mean", a "bad woman" and a "bitch" who turned good boyfriends into bad people.
In calls to his relatives from custody, he estimated he only remembered about five per cent of the attack.
"I'm glad I don't remember. The bits I do remember are so horrible," he said.
Acting Justice Hidden said it was tragic the attack took place when Ms Mottram had achieved some stability in her life.
"A dreadful crime has been committed by a very troubled young man," he said.
Mottram will be eligible for parole in April 2029.