LEIGH SALES, PRESENTER: Today's 20th anniversary of the Port Arthur Massacre has sparked much discussion of Australia's national gun control laws and warnings to ward against complacency.

Against that backdrop, it may disturb some people to learn that a shotgun with high ammunition capacity is now doing the rounds of collectors and shooters.

Last year 7.30 reported on the imminent arrival of the Adler gun in Australia, and soon after the story aired, the Government announced it was suspending importations.

But as Dylan Welch reports, the ban hasn't stopped the gun's appearance and in some cases it's being modified to an even higher capacity than originally designed.

NIK HALLIWELL, , GUN MODIFIER: Alright. If you want to count out seven rounds, we'll load it up, we'll go from seven.

DYLAN WELCH, REPORTER: OK.

Under Australia's importation laws, this shouldn't be happening.

NIK HALLIWELL: That's the sixth magical one. Seven. Alright, do you want to take a step back? Here we go. Ya ready? (Fires gun) That's it, we're all clear.

DYLAN WELCH: So that was seven cartridges, the original design?

NIK HALLIWELL: Yep that was seven in the magazine, but none in the chamber, so as it was originally designed coming out of the factory.

DYLAN WELCH: Adelaide gunsmith Nik Halliwell's firing the Adler Lever Action Shotgun. It's been modified to get around the suspension of the importation of the seven or eight-shot Adler.

NIK HALLIWELL: That was straight seven shots in about 10 to 12 seconds, so it's not as rapid as you might expect.

DYLAN WELCH: The gun has infuriated Australia's gun control lobby, which believes it's an attempt to undermine the 1996 National Firearms Agreement reached following the Port Arthur massacre.

ROLAND BROWNE, GUN CONTROL AUSTRALIA: They are a military type of gun and they have no place in a civilian society. John Howard moved Australia towards having shotguns with a maximum of two cartridges at a time. That's the safest position for Australia. We don't need people really setting themselves up as Rambo in the suburbs with weapons like this.

ROBERT BROWN, SHOOTERS, FISHERS & FARMERS PARTY: That is one of the most ridiculous comments I've ever heard. It is not a military-type firearm. It is a - what the Americans would call a sporting firearm. Most of the people, I assume, who would have bought it in Australia would have bought it for pig hunting.

DYLAN WELCH (July, 2015): It can fire eight shots in as many seconds using a firing mechanism straight from the Wild West.

Two weeks after we aired this story last year, then-Prime Minister Tony Abbott announced he was banning the importation of the gun due to its high magazine capacity.

It was a small inconvenience for the gun's importer, Robert Nioa. He quickly imported thousands of Adlers with a five-shot capacity that is easily modifiable to take more rounds.

NIK HALLIWELL: Hey, good morning. How you doing?

DYLAN WELCH: Good.

NIK HALLIWELL: Come in, come in.

DYLAN WELCH: Thank you.

Nik Halliwell runs a gun-modification workshop in the Adelaide suburbs.

NIK HALLIWELL: I've spent 20 years in the trade as a precision machinist running an outworking for several large companies. I've also worked for the military as well doing an support Armoured Corps role in that. I used to gunsmith for other people professionally and decided to break away and start my own company.

DYLAN WELCH: He's an industry expert being consulted by the state Police Minister regarding changes to firearms regulations. He's also one of the few people in Australia able and willing to legally modify the Adler five-shot gun to an eight or 11-shot firearm. His decision has attracted controversy and this is the first time he's spoken publicly.

So this is the magazine, the stock standard magazine?

NIK HALLIWELL: Yep, that's the standard tubular magazine underneath. What basically happens with these is this is currently a five-shot capacity and to pull it apart, give it a bit of a wiggle just lightly and we just keep pulling and then it comes out. And with an extension piece on, they're gonna sit roughly about there, so it's gonna extended it by about - by about two extra shells.

DYLAN WELCH: Modifying the gun takes Nik Halliwell about 10 minutes. This piece of tubing allows the gun to fire an extra two shells before reloading and turns it into the banned gun. It's so easy, he also emails three-page do-it-yourself guides to people who know their guns.

For months, owners of the Adler have been talking about modifications.

ADLER GUN OWNER: It would be really nice if they'd allow us to get the, um, eight-shot magazine. I believe there's some companies already doing extension tubes for them ...

DYLAN WELCH: While the Federal Government has temporarily banned importation of the seven-round Adler, most states have no restriction on how many rounds you can have in a lever-action shotgun, which means when Nik Halliwell modifies the five-round Adler, it's perfectly legal.

NIK HALLIWELL: All I'm doing is using state and territory laws quite openly and it's quite clearly stated in the law that we're allowed to do this. It's quite permitted.

DYLAN WELCH: But his work's still controversial given the import ban. It's come to the attention of police in other states and politicians opposed to the gun.

NICK MCKIM, GREENS SENATOR: The intent of the 12-month ban was very clear. We now understand that there are people working around that by engaging in modifications of magazines to allow for more shots than is currently covered in the import ban and we would like to see a lot of these loopholes cleared up, tightened up.

DYLAN WELCH: But Australia's most powerful pro-gun political party, the Shooters, Fishers and Farmers Party, disagrees.

ROBERT BROWN: If it's legal in South Australia and he's not prosecuted, I can say to you that it doesn't really matter from a public safety point of view how many rounds they can change the magazine over.

JOHN HOWARD, THEN PRIME MINISTER (June 6, 1996): I'm sorry about that, but there is no other way - there is no other way!

DYLAN WELCH: In the wake of Martin Bryant's murderous rampage, John Howard convinced all Australian states to enact identical legislation which tightened gun ownership controls and restricted access to some rapid-fire guns. Gun Control Australia says the Adler threatens that hard-won accord.

ROLAND BROWNE: It's a breach of the spirit of the 1996 Port Arthur round of gun laws that came in following the massacre and it needs to be banned in Australia.

JOURNALIST: This idea that it's contrary to the spirit of the '96 agreement, what do you say to that?

ROBERT BROWN: So what? Who cares? We don't want the '96 agreement. The '96 agreement, as I've just said, was a piece of garbage. It should be - it should be torn up. The states had before 1996 very strict firearm laws. Yeah, it went bad in Tasmania, very bad, but every state had the capacity then to do what they thought they needed to do.

DYLAN WELCH: 7.30's been told that gun owners using more powerful guns in the heavily restricted firearms category C and D are switching to the Adler, which sits in the less-restricted category A.

Would you choose this shotgun if you were a professional shooter or a farmer?

NIK HALLIWELL: A lot of the professional shooters C and D class that I work with who run, say, a pump-action C-class shotgun, they're actually converting to these as a category A because they can have more shots, so if they're culling from helicopters or chasing down pigs and dogs, it makes it easier for them to get repeated shots.

DYLAN WELCH: The gun is set to cause controversy for months yet with concerns the importation ban due to expire in August will lapse before the Government has made a final decision about what to do with the Adler.

LEIGH SALES: Dylan Welch reporting.