Grendel as a Universal Infantry Cartridge

[stanc]

The 7x46 UIC would be a bit too much for space utilization, weight, and recoil for the common assault rifle.

It's no worse in that regard than the .280 British, which many still point to as what should've been adopted instead of 7.62 NATO.

...you simply can't mitigate the requirements for a close-in weapon and an LMG with the same loading.

The trouble with that idea is it is contradicted by history. During WWII the M1 Garand was used for close combat, and it fired the same loading as the M1919 LMG.

We could eliminate some of the logistics and over-diversification issue with a universal LMG, that fills the role of the SAW and the 240 without losing the 240's downrange effectiveness. 6.5mm can do that with the right projectile and loading. A friend of mine is getting 2700fps with 139gr Scenars out of a Cz527 bolt action, so an LMG with no requirement to baby brass could get significant velocity with a load heavier than 120gr easily. 6.5mm bullets will always out-gas 7mm from smaller cartridges. You need significantly more powder to make even a 6.8 VLD match a 6.6 for trajectory, and you still lose the wind deflection contest.

All that's true, but you're still thinking conventional, lead-core bullets. With "green" 6.5mm bullets, you're looking at a max weight of ~120gr, and projectile length that eats up a lot of powder space. To get an optimum length, a 6.5mm bullet is going to be only ~100gr. That may be too light to achieve the desired terminal effects, especially at long range.

If 120-140gr is needed to achieve the requisite performance on target, it'll probably be necessary to use 6.8mm or 7mm, even if trajectory and wind drift suffers to some extent.