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.

They were technically functional but police say no suitable ammunition has been made for more than a century.

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

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

Police no charges have been laid at this stage.

Martin Cash gained notoriety in Van Diemen's Land after escaping from the Port Arthur penal colony.

He and an offsider targetted inns and wealthy landowners during a crime spree but were considered "gentlemen" bushrangers because they avoided violence.