A stolen pistol believed to have been used by Tasmanian bushranger Martin Cash has been recovered.

It was one of two mid-19th century black powder pistols stolen from Launceston's Queen Victoria Museum and Art Gallery earlier this month.

The firearms were taken after thieves smashed in a back door at the museum.

Police say the pistols were found buried just outside of Launceston, but will not say where.

A metal detector was used in the search, one of eight conducted in the past seven days in relation to thefts.

No claim has been made for a $5,000 reward offered last week for information leading to the pistols' return and a conviction.

The pistols are technically functional, but police say no suitable ammunition has been made for more than a century.

Detective Acting Sergeant Dwayne Kirkby says it looked like the offenders intended to go back and collect them.

"It appears the offenders have taken some steps to preserve the firearms," he said.

"They were wrapped up in cling wrap, or something similar, separately and tied up in a generic supermarket shopping bag."

No charges have been laid over the pistol thefts at this stage.

But police have charged a 22-year-old Ravenswood man over an unregistered, shortened .410 shotgun recovered in one of the searches.

The Launceston City Council say it is reviewing security at the museum.

Mayor Albert van Zetten says the pistols will not be handed back just yet.

"We need to ensure the security is adequate, it's showed that it hasn't been adequate - there's no doubt about that."

"We're working with other museums around the country to ensure that we can have the best possible security in place to ensure that this doesn't happen again," the mayor said.

Cash's career

Cash gained a reputation as a gentleman bushranger because he avoided unnecessary violence. ( Tasmanian Museum and Art Gallery )

Martin Cash was born in Ireland in 1808 and transported to Sydney for seven years after being convicted of housebreaking.

He left for Van Diemen's Land after being involved in cattle duffing.

But his life of crime continued and he was locked away in the notorious Port Arthur penal settlement after being convicted of larceny.

He escaped from there several times, later being joined by two others with whom he began a bushranging career.

They targeted inns and wealthy landowners, but earned a reputation as "gentlemen" because they avoided unnecessary violence.

Cash was captured on a visit to Hobart and sent to Norfolk Island for 10 years.

He later returned to Hobart and farmed at what is now suburban Glenorchy until he died in 1877.