MPs heard it is "frankly terrifying" that just 3% of gun certificate applications are turned down amid widespread failings.
One MP even said a constituent is in hiding because their ex has had his weapons returned to him.
The government is under pressure to tighten gun laws after a string of catastrophic errors came to light at an inquest into the Plymouth killings, which claimed five innocent lives.
Shadow policing minister Sarah Jones said a "casual approach" was dangerous and had proved fatal.
And Labour MP Rachael Maskell said a woman in her constituency had been forced into hiding in fear of her gun-owning former partner.
Ministers heard a fresh call for pump-action firearms to be banned from homes, and Ms Jones said a Labour government would carry out a full review of gun licensing laws.
Evil gunman Jake Davison murdered five people - his mum Maxine Davison, 51, Sophie Martyn, three, her dad Lee Martyn, 43, Stephen Washington, 59, and Katherine Shepherd, 66 - after his weapon was returned to him.
The killer, who took his own life, had a history of violence but had his weapon returned to him by police in July 2021 - the month before the sickening attacks.
Ms Jones told MPs: "There's no automatic right to bear arms and there's no right to be given the benefit of the doubt."
She said: "Devon and Cornwall now reject 6% of gun applications since the Keyham shooting, but the national average across England is only 3%.
"It's frankly terrifying to think other pump action shotguns could be in the wrong hands."
Tory policing minister Chris Philp said changes needed to protect the public would be made.
But Ms Maskell told the House: "I'm not reassured by the government's response."
She added: "I've got a constituent right now who's in hiding because her former partner has had his firearms returned to him."
In the aftermath of the shootings Labour's Luke Pollard - whose Plymouth, Sutton and Devonport constituency includes Keyham, where the killings happened - called for a string of changes to gun laws.
Among these would be a ban on keeping pump-action guns in homes and a national strategy to tackle the growing danger posed by incels.
He told MPs that he and his constituents were "angry", adding: "We've been failed locally by our police but nationally we've been failed by gun laws that need to be brought up to date."
In a statement released after the verdict, the families of the victims said Davison was granted a "licence to kill."
They said: "We firmly believe that these failings at Devon and Cornwall Police have resulted in the deaths of our loved ones. Warning signs were ignored and a license to kill was granted."
The statement added: "It is beyond us how Davison, a man with a known history of violence, mental health issues, and with no real need to own a firearm, was granted a licence to possess a gun in the first place.
"Davison then brutally battered two innocent children in an assault in the park. Davison's brutal attack was incorrectly categorised as a low-level assault. Following this attack, his firearms license was revoked and his gun was seized.
"Despite being charged with violently assaulting two innocent children, unbelievably, he was given his licence and gun back. Davison was considered a low risk by Devon and Cornwall Police.
"The evidence that we have heard from Devon and Cornwall Police was that of a system that was a shambles from the top to the bottom. Those in charge of making decisions as to who should possess a gun, had no training on how to do the job. There was no supervision of those individuals. There was no auditing of the decisions that were being made.
"There was a culture of granting people firearms licences against a background of serious concern. Davison's case was a prime example. These systemic failings with Devon and Cornwall Police have failed to protect the public. They failed to protect our loved ones."
Home Office minister Chris Philp said the coroner is expected to issue a prevention of future deaths report in which further recommendations are likely to be made.
He said: "We must ensure our controls on firearms are as robust as possible and learn the lessons of the tragic deaths in Keyham, and also in Scotland, and we therefore await the coroner's anticipated report into the prevention of future deaths with keen interest.
"We will respond to the expected coroner's report on preventing future deaths and the recent report by the Scottish Affairs Committee following the shootings in Skye and the IOPC report within 60 days of the receiving the last of those reports, which is going to be the coroner's report, and we will respond substantively to the recommendations in all three reports.
"I commit today that any further changes needed to protect the public will be made."
