Police said five persons were arrested in connection with the arms racket from the two states.
One person called Mukesh Kumar, a resident of Munger,the place notorious for manufacturing of illegal arms, was arrested from here and 50 ready to assemble pistols were recovered from his possession
Four others were arrested from Jharkhand.
"Kumar is a veteran arms supplier. Based on his interrogation, we arrested four other arms suppliers Rakesh Sharma, Afroz Alam, Miraj Alam and Ibrar from Adityapur Industrial Area from Seraikela-Kharswan district in Jharkhand. Our men recovered another 102 pistols from them," Inspector General (IG Operations) of Bihar police, Amit Kumar said.
Several milling, drilling and lathe machines, as well as other equipment were seized by the police personnel from the factory. An FIR has been filed in the local police station, he said.
"We had been gathering intelligence on this gang for sometime as it was very active in this region. It used to disassemble pistols and carry them unnoticed via rail routes all over Bihar and neighbouring states," Kumar said.
In Jamshedpur DIG (Kolkhan), Md Nehal told newsmen that the possibility of some arms manufactured in the unit being sold to extremists and criminal groups could not be ruled out.
The gang's marketing network was also being investigated, he added.
In two other raids, conducted at Barachatti police station area of Maoist-infested Gaya district, the STF seized 8 kg of opium, 400 kg ganja, a rifle and a country-made pistol.
Altogether nine persons have been arrested in this connection, the police added.