Are you talking about headstamp FLB?
If so it is excellant ammo. Noncorrosive, Berdan primed, safe, reliable, accurate, and clean burning.
I have not chronographed any, but I have been told that it is NATO spec ammo, even though Argentina is not/was not a NATO member.
I am saving my FLB and have started shooting DAG and MEN.
Dwight most of the Argentinian 7.62x51 FLB I have is 83. It is good ammo.
Have you bought this ammo already, or is it some that you have located somewhere?