We’re gonna need to start a NonCredible War College, lol, if you keep dropping write ups like that!

I am in an unusually altered state. I normally don't essaypost like this.

what I’m proposing is that you’d just have different kinds of battalions.

This is somewhat similar to India which uses a lot of 7.62x39mm AK-203s and 7.62x51mm SiG-716, distributing them to different units. However, India is primarily concerned with protecting its borders rather than preparing for hypothetical military force projections so they have a more stable idea of what weapons will be used where.

For the US I still do not think making battle rifle specific units is a good idea. It presumes a fully battle rifle equipped unit is ideal in a given situation. I don't think that's right. While 5.56mm can struggle at 600-800m (depending on the weapon specifics, ammo specifics, and who you ask), the presumption that even in the mountains of Afghanistan that this was a debilitating problem is overblown. Full power MGs and DMRs can work on the longer ranges, and inside of the extreme ranges intermediate caliber just gets better and better compared to full power for a service rifle. It is not as if every firefight in Afghanistan was at 800m.

Now, something that makes sense and has been done in the past is creating accurized 5.56mm rifles for units specializing in longer ranges. The USMC made the SAM-R and the US Army's 3rd ID made the SDM-R. Both of them were 20 inch barrel, M16A4 derived weapons that were modified, assembled with care, and given appropriate optics. If you want a "Mountaineer" outfitted unit, such a rifle makes a lot of sense as the service rifle as it prioritizes range without sacrificing ammo and parts compatibility with everyone else, and those rifles are a lot more usable inside of longer distances than a battle rifle would be. And still assuming this hypothetical unit still has all the full power DMRs and MGs backing up the smaller rifles.

Like, if you’re not mounted, or not mounted as often, maybe you can make an argument that cutting out a SAW gunner, and instead just having enough ammo, in general, to do collective suppressive fire… this is worth it as you are overall less equipment heavy in an unmounted, on foot situation, because you gain mobility and endurance/stamina, as a unit.

This was literally the TO&E in Vietnam. In WW2, there was a squad automatic rifle (usually the BAR) organic to squads. After WW2, the US first tried the idea of M14 equipped troops supported by an M15/M14E2 squad automatic rifle taking the place of the BAR. When the M14 was replaced by the M16, the squad automatic rifle role was removed because hey every soldier could do that job in a pinch with their controllable, full auto service rifle. This looked good on paper, but eventually resulted in the M249 SAW and that role coming back because a weapon that could be the base of fire organic in the squads was important. (This is partially btw why I am convinced the USMC is going to pull their M249s out of storage the second they deploy for force-on-force in the future)

If you are dismounted a lot, there's also a half decent chance you are on the strained end of the supply chain. You want to be able to carry more ammo per pound, not less. Suppressing fire is how firefights go. It is how people are trained. It is how they will fight. Dave Grossman is a fraud. The idea sometimes floated that soldiers with less ammo (because they are carrying bigger full power rounds) will compensate by firing more accurately and using fewer rounds is the opposite of pretty much every study I know of and of doctrine developed from studies and experience. More ammo is good, and a soldier can carry more intermediate ammo than full power ammo.

And yeah… yeah having a guided 40mm would be pretty neat, in a lot of situations.

Guided 40mm exists...somewhere. The Raytheon Pike was hyped for a while. What I mean by these rounds not materializing is, that they are essentially cryptids. People have photos of them, and maybe even they'll drunkenly tell you a story of how they touched one once, but they aren't just out and about. If a US infantry unit deployed tomorrow, none of the grenadiers would have any.