Military-style semi-automatics and centrefire rifles were banned after the March 15 terror attacks, bar a few carve-outs for pest control and gun collectors.
Associate Justice Minister (Firearms) Nicole McKee has repeatedly said more than 6600 New Zealanders are licensed to possess semi-automatics.
RNZ has sought clarification from Te Tari Pūreke Firearms Safety Authority about the data the police business unit holds.
It confirmed 6847 licence holders have a firearms endorsement to hold special classes of arms items.
However, only a fraction - 1593 - can hold the firearms banned by the Labour-New Zealand First coalition in 2019.
Of that number, only 328 people - pest controllers - can fire them.
The rest with prohibited endorsements have firearms for collector, theatrical or heirloom purposes and have to store a vital piece of their guns at a separate address, making them inoperable.
The bulk of the 6847 endorsements account for pistols. The Christchurch shooter was not carrying a pistol.
"Clearly she is using these figures to try and suggest that semi-automatic firearms are already widely available when they're not," he said.
"That goes to the heart of why I don't believe a gun lobbyist should be in charge of the firearms reform legislation or a review of the firearms registry."
Gun Control NZ co-founder Philippa Yasbek said she could not reconcile the minister's figure of 6600, pointing to another, much smaller number McKee gave in an answer to a written parliamentary question in February.
At that time, McKee said there were 1678 firearms licences endorsed to possess prohibited firearms.
"The number of unique persons is likely to be lower, as one person may hold multiple endorsements," she said.
Yasbek said if McKee had given the 6600 figure once, been "challenged and corrected", it could be put down to an honest mistake.
"But I think it's very odd she's given Parliament two different numbers for the same thing and appears not to have made any corrections when asked for further detail on that."
McKee has denied her comments were misleading, standing by the 6600 figure.
"To solely focus on the 328 endorsements issued to firearms licence holders for the purposes of pest control activity downplays the potential of others to legally access, possess and use prohibited firearms," she said.
"The issue we should be focusing on is access, not use, and this is why there is a need for the licensing system to stringently vet the fit and proper status of individuals."
Cahill said McKee's comments were a distraction from a debate that was supposed to be about what most people knew as the now-banned military-style semi-automatics.
"What New Zealanders were concerned about, and what was banned, was semi-automatic assault rifles such as those used in the Aramoana and Christchurch mosque massacres.
"That's still the case and here are only 328 people licensed to use those in New Zealand. I think it's important we stick to talking about apples and apples."
The Arms Act will be overhauled this term, with legislation expected to be introduced to Parliament in the next year.
