That states a 20 inch barrel - standard for 7.62x39mm. 300 BLK velocities are always given for 16 inch barrels.
There is no 7.62x39mm factory load which has more energy than 300 BLK past 120 yards. I am not guessing - I checked. And 300 BLK has 16.7% more energy at 300 meters.
