How could or should the 6.5 mm Grendel be improved?

[JASmith]

...But if an extended 6.8 mm x 45 case were used instead, the round would have an even smaller diameter allowing more to be fitted into a standard magazine.

The 6.8x45 case is too long for the kind of bullets we would need for long range effectiveness in a 6.5 when we keep the length short enough to operate in the AR-15 class of rifles.

It would, however be very interesting when taking advantage of the length provided by the AR-10 magazine well.

That raises the question of ground rules for this new cartridge. Are we restricting to the AR-15? Are we allowing AR-10 rifles? Or, are we assuming an entirely new rifle?

I know that much of this material was covered in Tony Woilliams' MG&A forum a couple or three years ago. It seemed that the group converged on something like a modern version the 6.5mm Carcano with cartridges derived from the 25 & .30 Remington running a close second. That discussion presumed a new rifle design optimized around the cartridge.

The ground rules will make a difference in both the optimization path and the feasibility argument.