Which is better? Or, which packs more punch. Depending on your purpose of the caliber, one caliber may be a better fit than the other. So for instances the 6.8 allows you to use heavier bullets, 165-175 grains than the 6.5 Creedmoor.
The heavier the bullet usually means the penetration will be more. For the ammo geeks, at 500 yards, 6.8mm will have about 60% more energy.
The 6.5mm Creedmoor with 142-grain have 2,061 foot pounds of energy at 100 yards, incrementally at 1,844 ft-bls at 200 yards, 1,645 ft-lbs at 300 yards, 1,463 ft-lbs at 400 yards, 1,297ft-lbs at 500 yards and 685 ft-lbs at 1,000 yards. The trajectory drop can be from 1.2 inches high at 50 yards to 63.1 inches low at 500 yards. Yeh, thats a lot, but the tradeoff is that the felt recoil is much lower than the 6.8mm. But its still good enough to take down a whitetail and at 1,500 foot pouds can bring an elk down as well.
This 6.5 is greatly embraced by the long range competitive shooter.
6.8mm – This is the newest caliber to enter this group, the military has adopted the round, slated for full deployment in the first quarter of 2023. This caliber is considered a short magnum, extremely accurate. This caliber is bigger than the 6.5.
Winchester states the bullet at 165-grain has 2,902 ft-lbs of energy at 100 yards, 2,605 ft-lbs at 200 yards, 2,333 ft-lbs at 300 yards, 2,084 ft-lbs at 400 yards, 1,865 ft-lbs at 500 yards and finally with 996 ft-lbs at 1,000 yards.
Though the caliber has more recoil, it is manageable. With its higher performance benchmark, this does cost more than the 6.5mm.