For those outside of New Zealand here is brief rundown on our gun laws.
Guns and ammunition in NZ can only be obtained by someone with a firearms license. Once you have a license there is no limit on how many guns you can own or how much ammo you keep. However you are limited to the types of guns you own by your license category.
A category: This is what the shooter had. Guns must be over 30 inches long over all. No automatics. Semi-autos must be limited to 7 round capacity, no flash hiders, stock must be fixed to grip (no pistol grip).
B Category: Pistols. You must be a member of a pistol club. You must have increased security.
C category: Collectors license. You can have anything, but never fire it ever.
E category: Military style semi automatic. No restrictions on semiautos. But you must join a shooting club that requires a non-restricted weapon. Mostly for milsim shooting competitions.
All categories require a background check. An interview at your house concerning you and anyone that lives there. An interview with a friend that doesn’t live with you. A check of your security/safe. A valid reason for ownership relevant to the category. Any indication of self defense is a fail. Random house checks at anytime by police.
The problem with a-cat is you can buy a restricted ar15, then buy parts and a large magazine to make it unrestricted. I’ve seen restricted parts sold as airsoft parts.