7.62x51 is heavy in bulk, has a lot more recoil, and more muzzle blast. You don't want all that indoors. It's not just a question of ballistics. That's why this is a "General Purpose" round.Looking at the new 6.8 millimeter General Purpose Cartridge design I really do not see much advantages to it over the 7.62 x 51. Bullet drop might be a little less than the 7.62 millimeter at longer ranges but that is it. I read the bullet weight on the 6.8 millimeter round is 140 grains. Bullet weight on 7.62 x 51 is 147 grain. They should have went with about 120 grain bullets in my opinion.
Maybe nothing is set yet and they are still experimenting but to me it just looks like someone just trying to make $$$ off of a government contract. They should have just went back to 7.62 x 51 if they are going to go with a 140 grain bullet on the 6.8 millimeter round.
The best tool for every situation is not always the biggest hammer you can find.