The Corps is actually ahead of the Army in finally adopting a replacement for the M16 that doesn’t have the stupid direct impingement/pistonless action. The Marines adopted the M27 as the new Infantry Automatic Rifle to replace the M249, and now they’re just rolling it out to everyone as replacements for the M16 in the regular infantry rifle and the DMR roles too. It is also replacing the M4A1 in Marine Corps service, being chosen to be the standard issue rifle for every 0311.
https://en.wikipedia.org/wiki/M27_Infantry_Automatic_Rifle
That’s an assumption not based on much of anything really important. DI vice off balance piston driven is a poor tradeoff. Look around at the rest of the AR world- indirect piston stuff is at its death knell. Offset torque eats BCGs and uppers , has poorer accuracy, kills free floated advantages (in mot all cases) and really does not solve any problems that are supposed to exist. The recent competitions for reliability and longevity still favor the original design- M4s still go 8500 rounds before failure ( for perspective, the venerable M14 was deigned to meet 1200 MRBF....) So, if one thinks that having a rifle that can realistically shoot 50+ mags of ball ammo before failing ( w/o maintenance of any type) then the AR15 sucks.
The boutique FNs and HKs all are gone from inventory- they didn’t meet the cut while the M16A4, M4s and Mk1XXXs all run and kill...
The M27 is yet to be really proven, God Bless the Marines.