Well there is always the Armalite AR-18, or the Stoner System. With lessons learned from the field, and some of the civilian adaptations of the those weapons.
The fact that they use mostly steel which is more plentiful then aluminum. The Are Mostly of a stamped construction making them easier to manufacture. I could see that the Stoner system if there are any of the old school left from the USMC and the Navy (SEALS) that were in Vietnam and remember the Liking of that weapon. With some light refinements and corrections they could both be viable weapons.
AR-18 Easy to maintain, mags, ammo, sights, and changing mags drill would be the same if you adopted the civilian AR-180 lower designs to it.
Stoner M22 and M23 Rifle and Carbine if you used the magwell from the Robinson Arms M-96 rifle, or heck yet, just fully develope the Robinson arms M96 to the full kit that the Stoner sytem was.
That way as with the AR-18 Mags, ammo, sights, and changing mag drills are the same.
I would likely see the Stoner/Robinson being the one. The parts commonality with the carbine/rifle/automatic rifle(Bren top mag fed version)/LMG/MMG. It would be easy to add a designated marksman model to this bunch.
Actually it might even carry the designation for the system as SR for the Stoner Robinson.
Carbine SR-1C
Rifle SR-1R
Auto Rifle SR-1A
Light Machine gun SR-1L
Medium Machine gun SR-1M
Marksman Rifle SR-1D
Either the AR-18 or the Stoner/Robinson could become the future United States AK
