The amnesty period runs for another three months - until August - but the buyback ends tomorrow.
Deputy commissioner Jevon McSkimming said police did not know exactly how many prohibited guns there were in circulation, but the numbers handed in had met their estimates.
About 1500 people were identified as possibly having prohibited guns.
Just over 600 have been handed in, including 152 pistol carbine conversions, and about 1700 parts.
McSkimming said not every person identified by police as possibly having a prohibited firearm would have one, and he was confident with how the buyback had run.
"This buyback has gone to plan," he said.
"It was a much smaller cohort with a known number of people. It was targeted for six month, we shortened the buyback part of it to three months projecting the scale of the people we thought were involved and I'm really happy with how police and the community has responded."
McSkimming said gun owners had been ready and willing to hand in their guns during the buyback process with no animosity from the firearms owner community over the amnesty and buyback.