There are questions being raised about how successful the gun buyback scheme has been.

The buy-back and amnesty ends today after five months of collection events.

Massey University defence and security studies fellow John Battersby says the 47,000 firearms handed in so far is quite a lot.

But told Tim Dower he suspects there are others in circulation.

"Because we have no register and because we haven't been paying much attention to the types of weapons coming into the country since 1983, we've got no idea how many are still out there."

However, he says it's likely police will catch up with those holding on to banned firearms.