>>64356479
The other solution is that of firepower and increased efficiency over 5.56.
The performance of 5.56 at typical engagement ranges is satisfactory, especially with a few heavier guns around. However, 5.56 is a rather inefficient cartridge. It was not made with our modern (70s) understanding of external ballistics in mind. By designing it around a more aerodynamic projectile, we can make it less powerful (= lower recoil, lighter weight) but still essentially equal energetically at 100 or so yards.
This was the premise of experimental cartridges like 5.56x38mm FABRL.
By employing even more weight reduction measures, we can end up with a cartridge around half the weight of brass-cased 5.56. Half the weight means twice as much ammo, and you can never have too much ammo.
>4.6-5.56mm
>again, a very light for caliber and length bullet, but around 30-40 gr this time.
>around 3000 fps
>higher pressures (75,000 psi)
>weight reduction

For both of these concepts, I endorse polymer cased telescoped ammunition technology, which was revived by the LSAT program and subsequently killed by the NGSW. I truly believe it's the way forward. Much lighter weight, better reliability, unparalleled temperature resistance (allowing for closed bolt machine guns), higher pressures up to 100,000 psi, cheaper manufacturing, and new weapon form factors are just some of its selling points. A gun in our second cartridge with a CT case might have an MP7-like form factor with a magazine in the grip because of how short its cartridges would be.