Superintendent of Police Arnab Ghosh today said they seized 48 firearms and a number of arms making equipment from the factory at Debipur village under Kaliachak police station area.
The firearms were of 9mm and 7mm variety.
During the raid last night, the police also arrested seven persons from the factory which was being operated from 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.