"[Conservation Minister] Eugenie Sage's tahr cullers are going to be using those guns. They couldn't possibly do the job without those firearms," he said.
Banning them would make owners hide them, restricting ownership to police and "bad guys". The firearms will become "grey" or "black" - partially or fully hidden.
"It's a minefield if they get it wrong and the guns go underground."
The retailer has been contacted by an older Springvale couple who feel guilty after the shootings and want to hand over their firearms.
"We shouldn't feel guilty. It wasn't us [who did the shooting]. It was a nutter," he said.
A police spokesman was unable to say how many others in Whanganui want to hand in semi-automatic weapons. Police have asked that those doing so ring to inform them, before arriving at a station.
The Chronicle has made an Official Information Act request, asking how many people in this area have firearms licenses that allow them to own semi-automatic and military-style automatic weapons and handguns.
The retailer, from Australia, remembers what happened there when there were gun amnesties there. A medical insurance levy was raised one per cent and the money was used to compensate people handing in their weapons.
"You should have seen the piles of guns they destroyed. Thousands and thousands."
He reckons if people handing in guns - including illegal ones - get a full amnesty and full compensation, 80 per cent would hand them over.
If there is no amnesty and no compensation, most will keep them. There are already reports of panic buying, ahead of changes to gun law.
Under current law people can get a standard category-A gun license after a character check, sitting a test and proving the gun will be stored securely. Those people can buy a range of semi-automatic firearms, ranging from .22 to .308, and in price from $1500 to $7000.
Semi-automatic shotguns are standard for the duck shooting season, which begins in May.
People with gun licenses who want a hand gun or a military-style automatic have to get an endorsement and a different category of license. A B-category license is needed for a handgun and the owner has to join a club and can only fire the pistol at the club.
A C-category license is for collectors, who can own guns but not fire them, and an E-category license is needed to own a military-style automatic rifle with a 30 shot magazine.
People with those have to say why they need them, and provide more secure storage.
"There's a lot of effort to get an E-category license. It will cost more than $1500," he said.
In New Zealand firearms license holders are registered, but their guns are not. Most countries, other than New Zealand, the United States and Canada, register the firearms.
