Ok, Evil_Edie and AlbertaSheepdog... I'll buy into the shoot and scoot arguments for unit tactics. But there must be a better platform/ammo combo available. Engagement distances past 300 yards are, largely, a thing of the past. So for the bulk of troops, a weapon/ammo combo that's effective past that distance is largely irrelevant. A good mix, on a unit level, is important - and that's a lesson the Soviets/Russians have taken to heart with the SVD/PSL platform, keeping a strong presence of the battle rifle as Designated Marksman weapon.
I like the concept of a 50/50 ratio, but I doubt that's realistic in a modern army. 25/75 would probably be more achievable.
So, maybe we should be arguing about what's the best option for the 75% ?
Given the following requirements, what would be your first choices, if $$ were no object? If adopted widely, the $$ issue is somewhat self resolving with mass production. It's largely a philosophical argument, for me. I'm past the age where running and gunning is a viable option (and I'll admit that's part of my bias), I'm thinking along the lines of "what would be the best option for our guys in uniform, who risk so much for us".
5.56x45 and 5.45x39 are, I would argue, not hard hitting enough. Shoot and scoot may be the objective, but I would think that if I were young, and scared, and in the thick of it, I would also want a round that stood a higher 1 shot drop probability. I get that everything is about compromises, but I think those two rounds are a couple compromises too far.
7.62x39 is a good, reliable round, but accuracy is an issue with the low velocity, especially past 200 yards, which brings it under that 300yard effective range that appears to be the general consensus as a minimum.
I guess, if we want to go there, let's build the "dream rifle" for the infantry. Sig 550 variant, G36 variant, Tavor, AK variant, etc. etc. Favorites?
Cartridge: Never shot it, but the performance of the 6.8SPC looks good on paper. 6.5 Grendel seems to be gaining some traction. What's the recoil like? Any other favourites out there?
I'll throw in my initial thoughts.
6.8SPC in either a Tavor platform (bull-pups give a nice, compact platform without sacrificing too much barrel length) or an AK platform (super reliability)...
6.5 Grendel might be better at longer ranges, but the 6.8 is better under 400yards, even at 500 yards (on paper), and works well with CQB short barrels, whereas the Grendel needs the longer barrels to stabilize.
Thoughts? I'm Ok with being proven wrong, that's how you learn.