The demonstration model (AK-200), presented to Russian Prime Minister Vladimir Putin during his official visit to inspect the products of the Izhmash arms manufacturing plant in Izhevsk, was apparently a basic AK-74 in standard 5.45×39mm caliber.
However, even the Vietnam era revised flak jacket was not really designed to stop an AK-47 round (a 7.62×39mm) fired at close range.
Since the 1960s NATO, the (former) Warsaw Pact, the People's Republic of China and other countries adapted relatively small sized, light weight, high velocity military intermediate service cartridges in the form of the 5.56×45mm NATO, Soviet 5.45×39mm and Chinese 5.8×42mm.