How could or should the 6.5 mm Grendel be improved?

[stanc]

Stan C, Thanks for correcting me on that.

You're welcome. I'd like to further suggest that, with no more than a one round difference in magazine capacity, the 6.5 Grendel case may be a better choice than the 6.8 SPC case. This is due to the weight and performance goals you seek.

Ammo Weight: IIRC, the Grendel case is slightly (~10 grains?) lighter than the SPC case. That's not much, but every little bit helps.

Weapon Weight: If new rifles and machine guns are designed to fit the cartridge, the shorter Grendel case would permit shorter -- and therefore slightly lighter -- weapons to be developed.

Ballistic Performance: As I understand it, a short, fat case allows better powder combustion than a long, slender case, thereby giving a slight edge to the Grendel case.