Testing, testing...

[stanc]

This is Grendel-class diameter - same as 7.62X39 and the 6.5x45 Czech within a 2-3 thousandths of an inch. Going down to say, the .422" of the 6.8 SPC / .25 Remington reduces the powder capacity a bit much, even if the COAL is the 2.80" allowable within the 7.62X51 envelope.

We will need this powder capacity to get adequate muzzle velocity...

Possibly. It depends on what you consider "adequate." The .277 muzzle velocity in the ballistics table ( http://www.65grendel.com/forum/showthrea...1#post6038 ) is a conservative estimate for the 6.8x43 case, based on available info and figuring an OAL of 2.4 inches. At 2600 fps MV, trajectory was very close to that of 7.62 M80, and wind drift was virtually the same.

Plus, Cris Murray's 7mm UIAC has a 46mm case length and OAL of 2.5 inches.

With these two examples, I fail to see any need to boost length beyond 2.4-2.5 inches.

Even so, we will be challenged to show that a 6-8 gram bullet of any caliber can be as effective as the 9.5 gram M80 round...

Perhaps so. We won't know until we do testing, testing...