A gun and ammunition was discovered at a huge 'million pound' cannabis factory in Cheetham Hill.
Police found more than 100 kilos of the drug when they raided a former mill.
Over a year, the 'highly organised' set up could produce a million pound's worth of cannabis, Manchester Crown Court heard.
Four Lithuanian men who were found at the mill at Park Place have all been jailed.
The men said they came to the UK in search of legitimate work.
One said they were taken to the cannabis farm from the airport.
Ramunas Lesauskas, 48, and Mindaugas Salys, 30, were jailed for two years, while Vincas Margevicius, 38, and Arturas Salkauskas, 54, were sentenced to 14 months.
A revolver and ammunition was found in a sofa in the mill.
The gun could only fire rubber bullets and blank cartridges.
Ammunition recovered included 'traumatic ball cartridges' and blank cartridges.
When police raided the mill on October 5 last year, they found Lesauskas, Salys, and Salkauskas in a living area which had beds and kitchen equipment.
Margevicius was found on the roof.
The cannabis farm included lights, a large industrial fan and ventilation.
Police believed a large crop had recently been harvested, prosecutor Alistair Reid said.
The court heard they each crop could be worth between £247,000 and £330,000.
"The premises was capable of producing four crops a year, thus making this a million pound per annum business," the judge, Recorder Ian Harris said.
"This was an extremely large cannabis operation.
"The premises was a fully fitted, finished and operating cannabis factory.
"It contained the hallmarks of serious criminal sophistication."
He told the four men: "It is clear to me that you were all trusted to be part of this enterprise, albeit not at a high level.
"None of you has previous convictions, but this is a high entry point into crime."
Salys came to the UK looking for construction work, but was met at the airport and taken to the mill to look after the cannabis plants, his barrister Peter Gilmour said.
Defending, Isobel Thomas said Lesauskas is a qualified HGV driver and was trying to find work but was also brought to Cheetham Hill.
The cannabis farm had already been set up, and he was given food and somewhere to live in exchange, she said.
Salkauskas and Margevicius had only been at the mill for a few days before the police arrived, the court heard.
Lesauskas and Salys both pleaded guilty to production of cannabis, possession of a prohibited weapon and possessing ammunition without a firearms certificate.
Salkauskas and Margevicius pleaded guilty to production of cannabis.
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