A man who brought a loaded pistol and a knife to a woman's home and held her captive has been convicted, but will walk free from jail within weeks.

Christopher Adam Duncan, 37, assaulted the woman he knew twice in early November 2021, throwing a bottle at her and lacerating her hand. She fled and hid in a cabinet within her western Sydney home, using a towel to stem the bleeding.

Returning a few days later, he then waved the gun at the woman, made threatening remarks, sliced her across the palm with the knife and then held her captive.

Initially considering jumping off the balcony to escape, she alerted passers-by to her predicament by dropping handwritten notes out the window.

"He has a gun," she wrote.

On Tuesday, Duncan was sentenced in Parramatta District Court over one count of assault occasioning actual bodily harm and one count of possessing an unauthorised firearm. He pleaded guilty to both counts on December 6 last year.

Judge Stephen Hanley took into account a further count of assault occasioning actual bodily harm and two charges of possessing unauthorised ammunition and acquiring ammunition subject to a prohibition order.

The judge imposed a maximum jail-term of 30 months, back-dated to Duncan's arrest on November 7, 2021, and expiring on May 6, 2024.

The self-taught mechanic will be released after a non-parole period of 17 months, expiring on April 6.

Judge Hanley noted the victim would have been "extremely frightened" by the assault which was aggravated by the fact a knife was used.

"There was threatened violence and actual violence and the injuries could have been more serious but fortunately were not," the judge said.

The judge noted there was no suggestion Duncan acquired the illegal firearm to use for other criminal purposes.

In imposing a longer non-parole period, Judge Hanley considered Duncan's "profoundly deprived" background which had led him to drugs, including methylamphetamine.

The 37-year-old's mental health issues stemming from his upbringing would be better treated in the community rather than in prison, Judge Hanley said.

Other mitigating factors included that he had shown remorse for what he had done, and had complied with instructions from corrective services since being in custody after his arrest.

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