A starter pistol which can easily be converted to a live gun and has been linked to three attempted murders will be illegal from June 4, the UK Association of Chief Police Officers (Acpo) said.
Imports of the Italian-manufactured Olympic .380 BBM were stopped last month, and Acpo urged anyone with this model to hand it in during an amnesty launched on Friday.
After June 4 the weapon will be prohibited under Section 5 of the Firearms Act 1968 and possessing it will lead to a mandatory prison sentence of five years.
Assistant Chief Constable Sue Fish, Acpo's lead on the criminal use of firearms, said a converted Olympic .380 BBM had "not yet" been used to kill but action was needed because it was so easy to convert.
She did not want to criminalise "the vast majority who purchased it quite legitimately" and appealed for those who bought the model to start races or for dog training to hand it in, saying: "The status of this firearm has changed."
David Penn, of the British Shooting Sports Council (BSSC), backed the amnesty.
"We are aware that many of our members may have purchased the Olympic .380 BBM for well-established legitimate uses. "The actions of a criminal minority have undermined the lawful use of this revolver and we appeal to anyone in possession of an Olympic .380 BBM to hand it to their nearest station."
He said the amnesty was also backed by the British Association for Shooting and Conservation and the Gun Trade Association and the organisations would work with Acpo to ensure members were not disadvantaged by the criminal minority who converted weapons.
Ms Fish said further reclassification of other starter pistols could not be ruled out at a later date but said the BBM had been singled out because "this one is easy to modify".
"It is the only one, to our knowledge, to date that has been used to cause significant harm through its criminal use," she said.
She added that 179 converted BBMs had been recovered since 2007 by 13 police forces in England and Wales.
"The bulk" were in London but weapons had been recovered across the country, including Bristol, Manchester and North Yorkshire.
The weapon had been used for offences causing serious physical harm and also in robberies, she said.
The fact that no deaths had been caused so far may have been because the sometimes poorly converted revolvers were often in the hands of inexperienced gunmen and were firing poor quality ammunition.
"There is a significant threat to public safety," she added.
"Our primary aim is to protect the public by removing this firearm from circulation."
Anyone with an Olympic .380 BBM is asked to hand it in at the front counter of a police station before midnight on June 4.
Mrs Fish said the BBM, which is manufactured by Bruni Guns, sold for between £60 and £80.
Around 1,500 are thought to have been imported into the UK since 2006 when the Violent Crime Reduction Act forced all realistic imitation firearms to be marked with a bright colour, in this case orange.
The BBM was defined as readily convertible after an independent test by the Forensic Science Service.
Its new status means no change in legislation is required to classify it as a prohibited weapon.
Handing in the pistol during the amnesty does not provide immunity to prosecution if it is found to be linked to a crime.