Armed officers carried out a warrant in Ellindon, Bretton, at about 4pm on Monday afternoon where they discovered the weapon, along with class A drugs.
Two men aged 20 and 58 were arrested on suspicion of possession of a firearm, along with a 49-year-old woman and a 15-year-old boy.
The 20-year-old man was also arrested on suspicion of possession with intent to supply class A drugs.
Information about drug dealing can be found on the force website here, https://www.cambs.police.uk/report/Report, along with the option to report information.
The 20-year-old man was also arrested on suspicion of possession with intent to supply class A drugs.