Apparently the Army’s choice of going to 6.8 mm is not the same as the old 6.8 spc that was tried by the Navy.
The two most significant attributes of the 6.8 TVCM cartridge are its enhanced exterior ballistics and lighter weight. The high muzzle velocity combined with the right projectile design is intended to provide over-match to commonly fielded body armor. The lighter weight will allow the individual soldier to carry more ammunition, and allow more ammunition to be transported to the battlefield for the same weight.
The new round is a 6.8mm x 51mm, same length as a .308/7.62, so the new rifle from Sig is more like an AR-10. Not sure about carrying more ammo; the magazines are 20 round capacity but they may increase that as the fielding process goes forward.