"Today's efforts surpassed the turnout on Saturday and I want to repeat my praise for both police and firearms owners who made this happen," Police Minister Stuart Nash said.
Feedback to police had been positive, he said.
Police on Saturday said they had one dispute about prices.
There are estimated to be about 14,000 people licensed to hold semi-automatics in New Zealand and the Government in June allocated $208m for the buyback.
However, with no formal registry of individual weapons, Treasury has warned the exact figures will be hard to predict and opponents have suggested the total cost could be significantly higher.
And not all gun owners are happy. The Council of Licenced Firearms Owners this week said it would join a fight against the legalisation and the buyback scheme.
Some owners have decried the pricing list that determines how much will be paid out for weapons, and the process behind it, but police have said they will not be budging.
The amnesty on weapons outlawed in the legislation runs until December. Owners who do not hand their banned semi-automatic rifles by then could face up to five years' jail.
The legislation, passed quickly and almost unanimously in Parliament, outlaws military-style semi-automatic weapons and assault rifles, though it includes exemptions for pest controllers, .22 rifles and pump action shotguns' smaller ammo capacity.