The school bus driver told police in 2021 that his drug-taking daughter and her partner were planning to crash a vehicle into his house, steal his weapons and abduct his grandchildren.
Concerns that the burglary could eventuate led police three months later to suspend his licence for a year.
The suspension was upgraded to a full revocation after police reviewed the case and it was discovered the man had told an MP that he had "never report anything to the police again ever".
"I do not believe that a person that makes such comments in response to police executing their duties, possesses the requisite foresight or consideration to have access to firearms," a NSW Police firearms registry official told the grandfather when he was notified of the decision to revoke his licence.
The man had written to Shooters, Fishers and Farmers MP Robert Borsak, saying the loss of his licence had eroded his trust in police.
"If anything untoward ever happens I'll report it after the fact," he said.
"They know how to put the law-abiding owners offside. I will never trust the police again. I've spent nearly 30 years staying out of trouble and they repay my good behaviour with this rubbish."
The man, who drives a bus for children with disabilities, later told the NSW Civil and Administrative Tribunal he was sorry for the letter and now realised it was wrong.
He said he had felt he was being punished for doing the right thing, having taken up competition shooting in recent years as an activity to share with his son.
Police defended their decision, pointing to the man's criminal history, which included stealing, assault, possession of unlicensed and shortened firearms and aggravated sexual assault.
But the man, who said he wasn't proud of his record, also said he was no longer the angry young man who acted out after surviving institutional abuse.
The tribunal on December 21 found the man to be candid, forthright and credible, and accepted he was now a responsible person and had respect for the law.
His letter to Mr Borsak was borne of frustration and the man would not conceal information from the police or deliberately not cooperate with them, the tribunal further accepted.
The tribunal rejected confidential police information as "largely historic (and) insubstantial" and dismissed the force's argument that the grandfather was not a fit and proper person to hold a gun licence.
Tribunal member Michael Griffin said the tribunal could "never be completely satisfied that there is no risk" in an applicant having a firearms licence.
But he was satisfied the risk was not so high as to stop the grandfather from holding a firearms licence.
The decision was one of more than 100 firearm licence challenges the tribunal dealt with in 2022.
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