By the look of it and the following it is an 7.62mm Round.
GUWAHATI: At least 2,000 Assam Police personnel, who were engaged in fighting militancy, carried their AK-47s without ammunition for nearly two years. The Comptroller and Auditor General (CAG) in its 2007-08 report revealed the Assam Police did not receive the ammunition till March last year.
The CAG report tabled in the state legislative assembly on Saturday stated that during 2004-05, the ministry of home affairs supplied 2,000 AK-47s at a cost of Rs 1.60 crore without any ammunition. The police department, after a lapse of nearly two years, placed an order for the supply of 3,25,976 rounds of 7.62 mm x 39 ball ammunition for the AK-47s valued at Rs 96 lakh with the Ordinance Factory at Bharangaon.
But the ammunition was not received till March, 2008. The report further said that in September 2008, the DGP said the ammunition could not be collected due to non-receipt of delivery and non-availability of railway wagons.
Ref: "India Times"