the new sig military round is very interesting....along with the polymer cases....when I heard 6.8 I thought ugh....because of the 6.8spc...but I guess they have done something totally different with it. really interested to see when they will introduce it to the civilian market.
I just saw some info on the new sig that will supposedly replace the M4, its actually pretty impressive. 2800 fps out of a shorter suppressed barrel, the 6.8X51 rd has a stainless steel bottom section that will accommodate 80,000 psi in the chamber, and will penetrate any current body armor. These are of course military rounds, not sure what civilians will have access to yet. AR's run in the 50-53,000 psi in the chamber at around 2800-3200 fps, depending on the load and the length of the barrel, for comparisons sake.
I can see it being applied within a team context, but the verdict is still out on replacing the M4 variants, you can carry twice the 5.56 ammo that you can the new guy, and the sig mags appear to be 20-25 rd mags and they are quite a bit heavier so you can only carry so much of it.
If you are in a setting that will require your team to put down suppressive fire on a group of morons you are trying to move in on, the new sigs are gonna blow through that pretty quickly, but having a few of the sig spears on the team would be a definite plus.
I can assure you that ammo will be stupid expensive, for longer than any of us hope..
Just thinking out loud....
Time will tell