ATTENTION, PLEASE !!
7.62x51 is the full metric designation for 7.62 NATO.
There is no such thing as .308 NATO. There IS a .308 Winchester.
Externally, the .308 and 7.62 NATO CARTRIDGES are the same. The CHAMBERS are different, as is the brass. NATO brass is thicker, so is smaller inside.
In general, you should not shoot .308 in a gun marked 7.62 NATO. You CAN shoot 7.62 NATO in a gun marked .308. If reloading cartridges, do not use .308 load data in 7.62 brass- pressures will be higher.
What we have here is... failure- to communicate.