The ammo supply chain is the reason.
We have tens of millions of 5.56mm rounds in variuos inventory locations.
Replacing/substituting that ammo means doubling the inventory for a considerable period, as weapons are switched out.
The rifles themselves would be the easy change.
New weapons are depot-level mods to the M-16/M-4 (and SAW?) to support the new caliber.
Personally, the 5.56mm caliber if fine.
Hits count.
Whenever I hear a guy say, “I pumped a full mag into him and he didn’t go down”, I think: “You missed.”
I really doubt the SCAR will be used in a modular role any more than the M-4. Nobody’s gonna carry a spare barrel. However, being able to switch out a barrel would be great for maintenance purposes. Should eliminate depot-level requirements.
Me too.