Kamaal Gibbs and Edward Roberts were both convicted and sentenced for concealing an Escort Magnum which was available for criminal associates.
Officers from West Midlands Police, acting on intelligence gathered, swooped on Gibbs' home on Birches Green Road in Erdington in March 2019.
They found the weapon underneath a shed and established the gun had previously been stolen from Northamptonshire.
Forensic testing found DNA from Gibbs on the shotgun along with fingerprints from Edward Roberts, with the latter’s DNA also on the ammunition.
Phone records showed Roberts had informed at least one known associate where the shotgun was stored and a subsequent search of his address found imitation handguns where work to convert them into viable firearms had been carried out.
There were tools which can be used in the process found at the property, although none of the handguns had been fully converted.
Roberts, 30, of Battleton Road in Evesham, pleaded guilty to charges of possession of both a firearm and ammunition with intent to enable another person to endanger life and possess articles for use in connection with the conversion of imitation firearms.
Gibbs, 23, was convicted of possession of a firearm, and possession of ammunition, with intent to enable another to endanger life.
Roberts was jailed for 11 years and 10 months and Gibbs for 10 years at Birmingham Crown Court on Friday, February 12.
Detective Sergeant Martin Kelly, from force CID, said: "A gun like this in the wrong hands could have fatal consequences.
"It was being hidden at the address but was known to be available to take.
"There is no evidence the gun was ever used but illegally possessing a firearm can lead to serious consequences and lengthy prison sentences."