A new law cracking down on illegal guns could see jail sentences of up to 10 years unless firearms certificates are updated.
It is now an offence to make, sell or buy a gun with a self-contained gas cartridge after Government laws were introduced on Wednesday.
Gun experts fear the weapons can be converted to take live ammunition and be used by criminals.
Now owners must apply for strict new firearms certificate within three months or face a prison term of between five and 10 years.
Licences can be obtained from a police station but officers have the right to remove the weapon if they believe the owner is likely to endanger public safety.
Peter Vaughan, assistant Chief Constable for Wiltshire, said: "This legislation has been introduced to take these types of weapons off the market, because it has been found that both the weapon and the cartridges used in the weapon could be easily converted to fire live ammunition.
"The legislation is designed to affect the supply of these weapons into criminal's hands, not to persecute members of the shooting fraternity, and assist in ensuring that Wiltshire remains as safe a county as is possible for us all to live in."
Gun owners and firearms retailers now have until May 1 to gain the proper legal paperwork.
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