Australian authorities are investigating whether a state police minister broke the law by firing two banned weapons at a prison's gun range.
New South Wales lawmaker David Elliott referred his own case to police after photos emerged showing him with the guns at a 2018 opening for the range.
Australia bans civilian use of semi-automatic and automatic weapons but exceptions can be made with permission.
Both Mr Elliott and prison officials blamed it on an "administrative error".
Australian media reported he fired a submachine gun and a semi-automatic pistol at the newly refurbished range in Sydney in September 2018.
In NSW, someone who uses an unauthorised firearm can be jailed for up to 14 years.
Opposition MPs criticised Mr Elliott for being unaware of legal requirements.
"You'd have to wonder what is going through the mind of a senior minister… to go and pick up a lethal weapon like this without checking if they had a lawful capacity to do that," said Greens lawmaker David Shoebridge.
Such weapons can be used by the military and elite police and prison officers.
Mr Elliott shared pictures from the event in a Facebook post at the time, saying he had dedicated the range to a prison guard who had died. Both he and the man's widow had fired an "official shot" in tribute, he added.
Mr Elliott said he had "acted in good faith" and used the weapons under "strict supervision", believing that prison authorities had signed off on necessary paperwork.
He said he contacted police this week after being advised the prison authority - Corrective Services NSW - may have potentially broken the law "with respect to potentially hundreds of individuals, including myself, who have used the range".
Corrective Services NSW apologised to Mr Elliott for "any embarrassment caused".
Mr Elliott, who is also the minister for emergency services, has been under fire from political opponents in recent times. In December he was criticised for holidaying in Europe during the state's bushfire crisis.
Australia introduced some of the world's toughest gun laws after a 1996 massacre, but experts say aspects have been softened in recent times.