A £1,000 reward is being offered to anyone who can help police officers find more guns.
More than 170 guns including rifles, revolvers and a First World War German handgun were surrendered to Northants police last month.
But inspector Sarah Johnson, who led the three-week amnesty, thinks there are more guns out there and people who failed to hand them in could be dangerous.
She said: “With those people who failed to hand in unregistered weapons during this period, I think it’s reasonable for us to consider their ownership of those items to be questionable.
“So I would encourage anyone who knows people who are still holding unregistered firearms to either contact us or Crimestoppers so we can remove those weapons from the streets and make Northamptonshire a safer place.”
Crimestoppers, which is backing the campaign, is offering up to £1,000 in reward for information which leads to an arrest and charge.
The chairman of Northants’ Crimestoppers committee James Shepherd Cross said: “We want the public to know that we take gun crime seriously and that, with their help, we can make Northamptonshire a safer place to live.
“Every anonymous call to Crimestoppers is potentially vital to preventing or solving serious crimes, and removing an illegally held firearm may save someone’s life.”
Anyone with information should call 101 or Crimestoppers anonymously on 0800 555111.
Alternatively, you can fill out a form here.
Information passed directly to the police will not qualify for the Crimestoppers reward.