Just watched a YouTube video comparing 5.56, 6.5 Grendel, 6.8SPC and .50 Beowulf. They were using Barnes bullets in gelatin and through barriers. Very interesting. They also showed the Kinetic Energy Transfer of each round on a graph. Judging by what the results were, J is right on the money. The Grendel has superior velocity at range than a 6.8 SPC. Under 300yds, the 6.8SPC is the winner as it dumps all its energy earlier during penetration than the Grendel.