A firearm owners lobby group claims the buyback process is not ending up how it was sold to the public.
An updated list of prohibited guns was issued on Thursday, with at least 100 new items added since June. New to the banned list are a number of AR-15 models, popular with mass shooters in the US.
"The latest buyback price list incorporates a number of firearms submitted by the public to police for consideration for the price list," police said in a statement.
Sixty-two weapons were added this week, including parts used by the Christchurch gunman, which were left off the original list of prohibited items.
"Police now considers that AR type lower receivers are prohibited under this Act," they told RNZ. "These substantive AR type parts can be used interchangeably and are capable of forming a prohibited firearm with a centre-fire upper receiver. Any modification of a prohibited firearm by replacing the upper receiver is not permanent and is therefore not consistent with the intent of the legislation."
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Nicole McKee from the Council of Licenced Firearm Owners says with just three months left of the amnesty, the list needs to be finalised.
"It's gone well-beyond the semi-automatic firearms the ban was meant to encompass. We find this of concern. We think the price is also of concern, the compensation package."
In total there are now 415 different banned guns eligible for compensation.
It was updated yesterday to total 415 banned guns and 47 parts.
"The legislation was so rushed, the police and Government were not able to put a full or appropriate figure to the amount of firearms that have been affected," said McKee.
No one is sure just how many guns are out there, with no centralised register. One will be implemented as a part of the Government's overhaul of New Zealand's gun laws following the March massacre in Christchurch.
"We have 250,000 people out there that need to know, one, their firearms are prohibited, and two, they will receive fair compensation for it," said McKee. "We need the list to be finalised."
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Retail stores like Gun City recently joined the buyback effort, after previously opposing the scheme.