People are being urged to hand in gas cartridge air weapons at Falmouth police station or face prosecution.
The "Brocock" air weapons, which use self-contained gas cartridges, are being criminalised and people have until May 1 to hand them in.
The government has brought in the new legislation because the cartridges these weapons fire can be converted into live ammunition.
After January 20 the weapons will be banned from shops and cannot be bought without a firearms certificate.
Police spokesman Sgt Alan Mobbs said: "While the law is relevant from January 20 there will be a period of grace until May 1, allowing those in possession to either surrender them at a police station or apply for the necessary firearm certificate."
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