The Federal Government has defended leasing out prime Sydney waterfront land to a sporting shooters' group at well below market price.

Finance Department documents have revealed the NSW Rifle Association pays around $510 a week to lease the 38-hectare Anzac Rifle Range on the Malabar Headland, around 12 kilometres south of the Sydney CBD, as part of a 50-year deal.

CoreLogic data showed the average yearly rent for a home in Malabar was around $1,000 a week.

Labor has written to the Auditor-General to ask him to investigate the deal and whether taxpayers were receiving value for money.

Labor has written to the Auditor-General to ask him to investigate the deal. ( ABC News: Adam Wyatt )

But in a statement, Finance Minister Mathias Cormann said it was a continuation of a previous lease.

"This site has been used as a shooting range for well over a hundred years and current arrangements are consistent with arrangements that have been in place for a very long time, including during Labor's period in Government," he said.

Coalition frontbencher Scott Ryan also brushed off suggestions of a quid pro quo deal with Liberal Democratic senator David Leyonhjelm over the lease.

But Senator Leyonhjelm has taken credit for the 50-year deal, saying the Government had lost twice in litigation over the future of the land before he intervened.

"It came as something of a relief to them to have someone like me turn up and say, 'I know this issue, I know the shooting association quite well, I know what their concerns and priorities are, I know the history of the range, I have a solution for you'," he said.

"It was almost as if they were waiting for me to arrive, in some respects."

The crossbench senator also said the deal helped the Finance Minister.

"It increased my goodwill towards the Government in general and particularly towards Minister Cormann, and so there've been times when he's called on me for support and I've given it to him as a result," he said.

But the Finance Minister said the new deal was similar to what was already in place.

"The arrangement in place now is substantially consistent with the arrangement that has been in place for decades," Senator Cormann said.

The property on the Malabar Headland includes four shooting ranges, a clubhouse, a caravan park and a car park.