Tactical Life posts that the military is changing to the 6.8 in SAW and M4

[A5BLASTER]

Look, here is the idea

6.5x39 (Grendel) would work with current M4 weapons requiring only a barrel and bolt swap.
6.5x45 would require a new rifle but is close to idea.
6.5x51 (260 Rem or 6.5 Creedmore) is too big

Not seeing the 6.8mm as anything but a compromise.

Also the .338NM (8.59x63 vs the .338LM/8.59x70) would make a good replacement for the 7.62x51 in the M240 series of MG

You forgot new mag for that 6.5x39 as well as new bolt and barrel. The 39 case and the grendel case. 2 different cases don't run throw 223/556 patterned mags.