When was the last time a military used the same cartridge for its rifles and sidearms?If you want to cull down your moving gear wouldn't you want a cartridge that both a handgun and a rifle could use. The old cowboys and drifters were on to something. Their pistols and rifles often used the same round. So to keep from having to have 9mm and 5.56, why wouldn't you use something like a 357 be choosen for ability to use 38++p hollow points ect.? Or something like that.
You either have an underpowered rifle or overpowered handgun.
I love the .357 Magnum round and have owned several revolvers in that caliber and it would be convenient to also own a lever gun or even a pistol caliber carbine AR chambered the same I can't see it being practical.