A buddy and I have both had serious problems with 50's dated Yugp 8mm ammo. I ordered 300 rounds - still have a couple hundred that I will pull down for the bullets - most have dimpled primers and wouldn't fire. My buddy perservered and shot his - took three or four tries on many of them.
I refer to it as the "new UN safety ammo".
The 70's dated Yugo, however, is superb! Hard to find now, but well worth looking for.