The licensed club run by officers from Belfast Harbour Police has been axed, and its weapons disposed of, following an investigation into its activities by Dr Michael Maguire.
Dr Maguire was called in by the Harbour Police's chief after unaccounted for ammunition was found in the possession of an officer.
His probe found that on a number of occasions until at least 2007, but not after 2009, practice shoots by the gun club had taken place at the same time as the force's official firearms training.
The police watchdog also discovered that gun club weapons and ammunition were stored in the same armoury as official police weapons within the Harbour Police premises at the Belfast Port Operations Centre.
Dr Maguire said: "This created an obvious potential for official police armaments to become mixed up with guns and ammunition privately owned by gun club members.
"Clearly this was inappropriate. It is vital that there are stringent accounting mechanisms to keep track of police weaponry and ammunition, as these will inevitably form part of any investigation into the use of a firearm by the Harbour Police."
The issue came to light in April 2012 when a routine check by the Harbour Police of its weapons and ammunition established that a police firearm and associated ammunition were missing.
Enquiries showed that a Harbour Police officer had signed out the weapon and ammunition, but had failed to properly check them back in on the firearms accounting register.
Any inaccuracies have the potential to frustrate and compromise investigations and due legal process.
Dr Michael Maguire
In an effort to find the missing items, the officer's locker was opened and a quantity of ammunition was discovered.
Later, it was established that the officer was authorised to have been in possession of all the ammunition, except six rounds.
The missing police firearm was later found in the police armoury and all official ammunition was accounted for.
When interviewed by Police Ombudsman investigators, the officer said the unauthorised rounds were likely to be from gun club stocks and he believed that the firearms certificate for the Harbour Police Gun Club entitled him to be in possession of them.
He said he believed he had obtained the rounds in 2007 during a joint gun club practice session and official Harbour Police firearms training, but denied having ever been in possession of the ammunition while on police duty.
The officer accepted that the rounds should not have been stored in his police locker.
A file was sent to the Public Prosecution Service at the completion of the Police Ombudsman's investigation.
However, it directed that the officer should not be prosecuted in respect of any criminal offences.
The Police Ombudsman subsequently recommended that the officer should be disciplined for breaching Harbour Police guidelines regarding the storage of unauthorised ammunition on police premises, and for failing to follow procedures for accounting for police armaments.
These recommendations were accepted and implemented by the Belfast Harbour Commissioners, who oversee the Harbour Police.
Dr Maguire also made a number of recommendations regarding Harbour Police armaments and urged PSNI Chief Constable Matt Baggott to review whether there was a continuing need for a gun club sanctioned to store privately owned weapons on police premises.
In addition, Belfast Harbour Police requested Mr Baggott to revoke the club's firearms licence.
The PSNI subsequently recovered the club's weapons and ammunition and arrangements were made for their disposal.
The Harbour Police officer who was investigated for unauthorised possession of ammunition also voluntarily surrendered the firearms licence for the gun club, which was then wound up.
A spokesman for organisation said: "Belfast Harbour Police has strict monitoring processes in place and proactively approached the Police Ombudsman when an issue was identified.
"We cooperated fully with the Police Ombudsman throughout the investigation and have implemented the recommendations in their totality."