As the title says, this is headstamped FDI.

In contrast to the M855, this headstamp features a sideways "V" vs a sideways "A".   

Both had a dot above them.

This follows the pattern of probably the same Indian manufacturer who produces the ammunition with the headstamp of SDI.

Post on IAA (https://forum.cartridgecollectors.org/t/indian-5-56x45mm/47098/4)