http://guntech.com/ammo/compare.jpg
here's a great pic for the rifle rounds. one thing important to note, the 5.56 is smaller than the 7.62, however because of the design of the 5.56 it does more damage to tissue. also the 7.62 has more bullet drop, but with the proper elevation, it will keep its velocity longer due to weight. that's why the iron sight on my mosin nagant goes out to 2000 meters, even though i prolly can't even see that far. it is my opinion that the 6.8 spc is a good personal defense round, good for close quarters, while the 6.5 grendel brings a little from both the 5.56 and the 7.62, and makes a good compromise of the two.