Australia has more than 3.5 million registered guns.
In addition to that, it's estimated there are a quarter-of-a-million undeclared weapons on the "grey market".
The number of licensed gun owners has nearly halved since 1997, the year after the Port Arthur Massacre, according to GunPolicy.org. But how effectively are they tracked across state and territory borders?
Last week three people – two police officers and a local resident – were gunned down at a remote property west of Brisbane.
The tragedy has renewed a push for a national gun register.
Queensland Police Union president Ian Leavers said the existing database was "chunky and cumbersome".
"When we’re talking about firearms and firearms holders who cross state boundaries, information is not readily available from their home jurisdiction," he said.
"Most Australians believe police have this information at their fingertips and we simply don’t."
Queensland's own firearms register was found to be "not accurate and up to date" and not "fit for purpose" by the State Auditor two years ago.
The report found the register relied on inefficient manual data entry and could not provide the real-time information necessary to support a modern risk and intelligence based regulatory function.
It found multiple examples of conflicting information between the Queensland police database QPRIME and the state firearms register.
In response, Queensland police said they set up a firearms oversight committee to implement the report's recommendations.
On Thursday, Deputy Commissioner Tracy Linford told reporters "significant improvements" were underway to the QPS registry.
What happened at Wieambilla?
Initially, police said they had attended the Wieambilla property for a missing person report for Nathaniel Train.
This week, an ABC investigation revealed Nathaniel Train had illegally crossed the state border from NSW into Queensland with guns a year before he, his brother Gareth Train and ex-wife Stacey Train, gunned down constables Matthew Arnold and Rachel McCrow, and neighbour Alan Dare.
Nathaniel Train's gun licence had also been suspended.
Police confirmed they had put out a warrant, which they attempted to serve multiple times before four young officers were sent to the rural property west of Brisbane last Monday.
On arrival, the officers were ambushed by Nathaniel, Gareth and Stacey Train.
Queensland Deputy Commissioner Tracy Linford said there were no "particular flags" about the killers, but police knew about the outstanding warrant from the border breach.
How would a national gun register work?
A national register may not necessarily have made a difference at Wiembilla, Mr Leavers said.
But he said it could help police in future decide whether or not to escalate their reaction.
"What I believe we need is a nationalised system which would record you being a licence holder, any weapons that you acquire, dispose of, have in your possession or that have been reported stolen [and] any offences which have been committed that relate to firearms," Mr Leavers said.
"This would give police valuable information in relation to the intelligence required to perform risk assessments which would assist them in keeping the community safe as well as themselves."
How do we track weapons now?
The Australian Criminal Intelligence Commission (ACIC) runs a national gun database, which Queensland police confirmed their officers use.
Deputy Commissioner Linford said improvements to the Australian Firearms Information Network (AFIN), and Queensland's own firearm database, were being considered.
Speaking at Thursday's press conference, she said police knew "very little" about the Trains before the shooting.
She said Nathaniel Train's only history was a 2014 driving offence, and Gareth Train had a 1998 offence for unlawful possession of a firearm, which had expired. Stacey Train had no criminal history.
ACIC calls its national database a reference tool to help police "identify and record firearms in a consistent way".
In a statement, ACIC said AFIN's purpose was "not to manage and regulate ownership and use" but to "improve information sharing" between states and territories.
States and territories are responsible for gun manufacture, licensing and use.
"AFIN allows state and territory firearms registries to maintain visibility of firearms and firearm holder's information – such as name and date of birth – and where they are registered when they move between state and territory registries," ACIC said in a statement.
The state's premier, police commissioner, and now Prime Minister Anthony Albanese have said they support a discussion on a new database.
Mr Albanese said on Tuesday he would be asking for a Cabinet briefing on how to "change the nature of the way that information if coordinated", and he was open to talking to state and territory governments "about how there can be a better national consistency and national information".
How many guns and gun owners are in Australia?
Police seized six weapons from the Wieambilla property after the shooting – two licensed to Nathaniel, three unregistered and one with an unknown owner.
There are more than 3.5 million registered firearms in Australia, according to data released last year by the University of Sydney's GunPolicy.org – an average of four for each licensed owner.
On top of that, there are about 260,000 illegal firearms, putting the number of guns owned nationally closer to 3.8 million, according to GunPolicy.org.
About three in 100 Australians are licensed gun owners.
Could a national register reduce gun crime?
Dr Samara McPhedran, from the University of Queensland, is an expert on gun violence and policy.
She said the police shooting last week was a "complicated set of circumstances".
"It's very challenging to speculate on what may or may not have occurred, whether there were intervention points, whether intelligence was shared as effectively as it could have been.
"Potentially we’re looking at a case where all the laws in the world wouldn’t make a difference, and what I’ve been saying for years – violence doesn’t occur in a vacuum," she said.
"We can’t fall into this easy trap of saying, 'we can police our way out of this'."
Gun laws can change with the "stroke of a pen" – but we need to understand why people commit violent crimes, she said.
And gun access is already "very tightly regulated".
"For any violent offender, there’s value in understanding what motivated them and also in this case there are going to be questions on operational police responses.
"It’s very easy to pick one thing and to focus on that – a national gun registry – that’s never going to offer the answers and getting the answers is a long, detailed, complex and challenging process."
