Optimum 6.5 Grendel bullet weights

[stanc]

I think that the only chance an intermediate round will have of being adopted by the military is if it is able to replace 7.62mm as well as 5.56mm, since that would provide significant advantages (especially ammo weight reduction).

While it would clearly provide a significant weight reduction for machine gunners, it'd mean a weight increase for riflemen. Not only would the ammo be at least 50% heavier than 5.56mm, it would (for US troops) likely necessitate a switch from lightweight aluminum magazines to heavier steel mags, further increasing the carry load. And it'd require a bigger, heavier rifle, too.

It is clear that the US Army wants lead-free ammo in the future and that the M855A1 EPR represents the currently favoured pattern so, whatever bullet weight is selected, the design should comply with this.

Concur.

I am not overly concerned with bullet weight as such, more with the ballistic coefficient. At the very least the BC should match the M80, which would mean that the muzzle velocity would have to do the same to match the long-range ballistics. Obviously, the better the BC, the more the MV could fall while still matching the M80 at long range. However, too low an MV could cause trajectory issues at short to medium ranges, so is not desirable.

As ever, there will not be one universally-agreed "right" solution to this conundrum, it's a matter of juggling various criteria to get the optimum compromise.

Precisely.