Officers from the regional organised crime unit Titan raided a lock-up garage in Morecambe, as well as a home and a farm outbuilding in Cumbria.
They found 10 guns and a large amount of ammunition.
A 49-year-old man has been arrested.
Among the weapons found were a loaded handgun, revolver, pistol, three disassembled shotguns, two disassembled bolt-action rifles and hundreds of rounds of ammunition.
Detective Superintendent Jason Hudson, head of operations at Titan, said: “This arrest and firearm seizures are a great result for the police and the community. We have taken ten dangerous weapons out of circulation and our enquiries are continuing into how they were obtained.
“I understand that people who live in these areas will be shocked and perhaps unnerved when they hear about the seizure of these weapons. However it is positive news that they have been removed from the community as firearms such as this can pose a very real danger if used illegally.
“Titan exists to target and take apart serious organised crime groups throughout the North-west and beyond and I am grateful to our colleagues in Cumbria and the NCA for helping to make this morning’s operation a significant success.”