An ammunition factory has been discovered by GMP in a Derbyshire town.
Police raided a house in Buxton today on a smart modern estate overlooking countryside.
The swoop in Walker Brow came after months of painstaking investigations.
The force has described the find as "significant" and is suspected of being a key supply line guns and ammunition to Greater Manchester's gangs.
Detectives seized ammunition, firearms components and "tools believed to be used in the manufacture of ammunition" in a raid at 8.30am.
In a statement Greater Manchester Police said: "At around 8.30am, officers from GMP's Serious and Organised Crime Group executed a warrant on Walker Brow in Buxton as part of an on-going investigation into the supply of firearms and ammunition.
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"Following a search, a quantity of ammunition, firearms components including barrels and other tools believed to have been used in the illegal manufacture of ammunition were seized.
"A 20-year-old man has been arrested on suspicion of possession of a firearm. He remains in custody at this time.
Detective Constable Christopher Chinnery, of GMP's Serious and Organised Crime Group, said: "This is a significant discovery as part of our commitment to tackle the use of firearms and gang-related crime in Greater Manchester.
"These items could have led to devastating consequences and we remain committed to tackling organised crime across Greater Manchester."
Police are currently dealing with a three-way gun war between two Cheetam Hill and one Salford gang.
It has seen a spate of shootings since November last year, with the most recent being in September in which a a 27-year-old man was hit multiple times after being shot at five times.
In Salford there have been five unconnected shootings since September, including three in a week last month.
But police have seized three firearms and bullets after carrying out sweeps of several locations in the city.