Police said the ammunition was smuggled from Myanmar by a man identified as Nang Go Tuang (56) who was arrested.
Tuang is a member of the Tahan B gang of Myanmar.
The smuggled bullets which would cost around Rs 12.50 lakh in the local market, were for US-made M-16 and domestically manufactured INSAS rifles, the police said.
The police were suspecting that the ammunition was meant for Chakma insurgents operating in Bangladesh or some North East insurgents operating in neighbouring States.