Acting on a tip-off, the police raided a place at Pathantuli village and busted the gun factory.
A gunmaker Md Nazrul, who hails from Munger in Bihar, was arrested from the illegal unit, the police said.
A total of 30 firearms comprising pistols and guns were seized from the place. Nearly 150 incomplete guns, gunmaking materials were also recovered from the spot.
Another college student was held for interrogation in this connection, police said.