[grylsyjaeger]

The 7.62x39mm may lose speed quicker and drop quickly over shorter distances than the 5.56x45mm but it has a higher ballistics coefficient due to nearly twice the projectile weight and will actually reach out farther and harder the 5.56x45mm.

But as Linda has said, the current service rifles use the 5.45x39mm round which like the 5.56x45mm tends to tumble as it hits a target due to being a front heavy projectile.