NSW Premier Chris Minns has admitted the government’s gun buyback scheme will result in some gun owners reimbursed for less than what their weapons are worth on the market.

Minns told the NSW upper house’s budget estimates committee on Thursday the government had no plans to change a “special exemption” allowing primary producers and sport shooters to own no more than 10 firearms, a portion of the policy that has attracted fierce criticism from farmers.

The state government announced on Monday it would join the federal government’s national gun buyback scheme – the only state to do so – and Minns has declared he was willing to make it an election issue. Opposition Leader Kellie Sloane this week labelled the buyback “half-baked” and a “very expensive solution to the wrong problem”.

The scheme, first announced after December’s Bondi Beach terror attack, is the largest buyback scheme since the one that followed the Port Arthur massacre in 1996, and will result in gun owners being paid between $450 and $1000 in exchange for their firearms.

Upper house Nationals member Sarah Mitchell told the premier that many gun owners would be left thousands of dollars out of pocket by the scheme because the value of their weapons was much higher than what the government was offering to pay.

Minns said he had done “my own research” on the recommended retail price for some firearms and “in many of the instances, it’s below the compensation that we’re asking for”.

“The schedule is such that in some instances it will be below the recommended retail price for the resale for the resale value, but it’s not in every instance,” he said.

Minns said the government had put in a special exemption cap for farmers and sporting shooters to hold 10, not four, guns, because it “wanted to reduce the net number of guns in the community”.

“We had to make a considered decision,” he said. “It’s not four, which is the general licence condition for guns, and we believe that this is the appropriate number in regional communities. Otherwise, it may get to the point where there’s no point in having the reform or the change.”

He did not answer questions from Mitchell about why the government decided 10 was an appropriate cap.

“We listened obviously to the farming community, and we believed that in agriculture, as was the case for sporting shooters, there needed to be a special exemption, not the minimum four, but it couldn’t be an infinite number,” he said.

“Many disagree with us, but at the end of the day, there needed to be a figure because if the figure was so astronomically high, it would make the whole policy redundant and not worth pursuing in the first place.”

He later added: “You deserve a straight answer. We’re not going to change the policy.”