Superintendent of Police Arnab Ghosh said 48 finished firearms and a large number of unfinished arms were seized from the factory at Debipur village under Kaliachak police station area.
The firearms were of 9mm and 7mm variety.
During the raid early today, the police also arrested seven persons from the factory which was being operated from the house, Ghosh said.
The arrested were the owner of the house and six persons from Munger in Bihar, known as a hub of illegal firearms manufacturing centre for long.
During search of the house, the police also seized suspected fake Indian currency notes with a face value of Rs 50,000.
It was being suspected that the arms manufactured there were delivered to neighbouring states.