They should have just gone back to a twenty inch barrel on the 5.56 and upped the pressure a bit. It never was a good idea to take a cartridge so dependent on velocity as the 5.56 and start turning out rifles with 16 and 14 inc barrels.
Sure, the new round gets high velocity out of a short barrel, but then you add six inches of suppressor and you are right back where you started.
M855 A1 works great out of 14.5 inches.
Wide spread adoption of optics has greatly reduced complaints about 5.56 effectiveness.
