Acting on information provided by two arms dealers, arrested earlier this week, a police team conducted a raid on the factory being run in east Kolkata's Tiljala area.
"Saurav Kumar, 19, Sonu, 22, Raju, 22 and Sarfaraz Alam, 24, were arrested from the factory and eight 7.65 mm semi-automatic improvised pistols, 16 magazines and 50 rounds of ammunition were seized," said an officer from Tiljala police station.
"Two big lathe machines, a barrel drilling machine, five clamp machines, two metal polishing machines and several other arms-making tools were also seized from the factory being run in a rented house," he added.
The two arms dealers from Bihar's Munger, whose information helped police nab the four, were arrested on July 24. They had revealed that they were a part of an illegal racket that manufactured arms by hiring labourers from Munger and sold them to dealers, who in turn sold them for Rs 35,000 to 50,000 per piece.