The compactness of the AR-15 has been a great limiting stick though to force the industry to develop higher performance cartridges that still fit within a magazine that is easy to carry on soldier’s load. Once you depart from that basic form factor for the magazine, the pouches and soldier’s load suffers. A lot of people might see this and only have reference to a mag pouch or two on their range belt, never having had to hump a basic load or basic load plus, in addition to all the rest of their duty position-specific equipment (Radios, Medic Bags, breaching tools, demo, Anti-Tank weapons, linked 7.62 on gun teams, tripods, T&E mechanism, 40mm Grenades, smoke grenades, grenades, Night Vision, etc.). This is why the 6.8x51 is an abortion even if they had a great weapon design, which they don’t.
This is why I have been more of an advocate for Grendel replacing 7.62 NATO. Similar concept as replacing 50 BMG with 338 Norma Mag.
5.56 is a very inefficient case that wastes a lot of powder, so it’s too long for what it delivers. We could replace 5.56 with something smaller in overall length, and deliver better performance with a look at bore diameter, case design, and propellant. KAC/Hornady already showed that with the 6x35 PDW. (.221 Fireball necked up). You can carry a bunch of those 6x35 KAC PDW mags, almost like M2 Carbine mags.
The .264 LICC is a good compromise getting us away from the 7.62 NATO form factor battle rifle cartridge though. It would be far superior in DM Carbines and LMGs, and would make a nice changeover with NATO coordination for a new set of weapons based on it in those roles. I think 5.56 will be around until the 2nd Coming though.
