Ramesh Kayam, a resident of Chakradharpur in adjoining West Singhbhum district, was arrested soon after he alighted from a train, DySP (law and order) Kanhaiya Upadhyay said.
Upadhyay said 55 live cartridges have been seized from him.
The cartridges are of 9mm bore, SLR and AK-47 rifle, he said.
The jawan was heading towards the Bagbera locality on the outskirts of the steel city to sell them when he was caught, he said.