Gun City's David Tipple told MPs today the Government's firearm law changes imposed "incredible infringements upon civil liberties", and that it could increase crime.
Mr Tipple was presenting on the second tranche of gun law reform, which he had earlier described as having the potential to create "the climate that the anti-gun lobby is so eager to avoid".
The Prime Minister announced the second tranche of proposed gun laws in July. It included the creation of a gun register, dropping the length of gun licences from 10 years to five and police being given additional powers to put warning flags over people.
1 NEWS was leaked a draft version of the legislation in August.
The registry would work in a similar way to vehicle registration, holding the name of the owner, date of birth and address, as well as the firearms licence number. It would be available online and include a paper-based option.
The changes came after the March 15 Christchurch terrorist attack, in which 51 people were killed.
Mr Tipple said the gun buyback was creating "thousands of lawbreakers" and that low trust in the Government was creating vigilantism.
"This problem is the erosion in trust of our Government and our courts and our police. This is the Dirty Harry problem. Once vigilantism is accepted, it is not just OK but deserved or necessary, the weapons used are irrelevant."
He said that "for years our firearms licensing system has effectively preventing the occurrence of such vigilante action".
Mr Tipple said he thought the Government had created "a whole lot more people who have less confidence in them".
"By reducing trust in Government, we are dividing the nation and we are driving them away from the unity we need here."
He also said it was a common misconception the US has a "gun problem".
"I believe Americans actually have a Dirty Harry problem."