Judge McDonald adopted a starting point of 10 years and arrived at an end sentence of seven years after appropriate discounts for factors such as early guilty pleas.
Cassidy was the driver of a motor vehicle on Kiripaka Rd, Tikipunga, just before midnight on September 2 last year when police attempted to stop the car for speeding.
He leaned out of the driver's window and fired one shot from a .303 bolt-action rifle at the police car, which had two officers inside.
The unarmed officers abandoned the pursuit and pulled over.
Cassidy's vehicle was seen by another police patrol a short time later and he led officers to Onerahi and on his way back into town, he drove in a dangerous manner along Riverside Dr.
His vehicle was successfully spiked but Cassidy continued to drive on three wheels.
He fired another shot at police and a third one while driving up Fire Brigade Hill that struck the left headlight of the police vehicle.
Cassidy and his alleged co-offender were arrested on Tarewa Rd.
Cassidy argued in the High Court that he fired the sawn-off rifle while leaning out of a moving vehicle, making it harder for him to aim at police officers.
His lawyer submitted that Judge McDonald should have focused on the excerpts of Cassidy's mother's letter that related to his exposure to gangs, violence and firearms "from a very young age".
But Justice Toogood said there was a determined persistence about his offending that could not be sufficiently linked to an upbringing in a gang-related environment so as to justify a significant discount for diminished moral culpability.
"Mr Cassidy was fortunate that his offending did not result in the serious physical injury or death of any of the police officers involved in pursuing him, or of an innocent bystander caught by a stray bullet or a vehicle, if it crashed," Justice Toogood said.
"The final round that struck the headlight of the police vehicle was close to going through the windscreen and could have struck an officer. Mr Cassidy's use of the firearm on several occasions throughout the pursuit adds to the seriousness of his offending, so a starting point at the higher end of the range was appropriate."
He said the rifle Cassidy used was a .303-calibre which, as Judge McDonald observed, was a powerful firearm designed to kill people and that the risk presented by the use of such a weapon was greater than those presented in cases where .22-calibre rifles were used.
Justice Toogood said Cassidy's offending was serious, violent and prolonged.
"He continued to try to evade police and use the high-powered firearm despite an extensive pursuit and efforts to disable his vehicle."
