Or a better round to make the current platform more effective. Either re-chamber everything for the 6.8mm SPC, assuming that rounds gets the imprimatur of the military establishment, or go for a 5.56mm version of the Russian hollow-cavity 5.45mm round. Most likely it'll end up being the 6.8mm SPC. It's being field-tested in modified SPRs now, or so I hear.
I'm hearing bad things about the M855 round from folks who've come back from overseas. Yes, it will hit what you aim at. However, in many cases it takes many hits from a 5.56mm weapon to bring a target down. In some cases people who have been hit and left for dead have gotten up again and returned to the fight...in one such incident the "victim" had been shot at point-blank range. This is not a good thing. It is not the weapon that is the cause of these problems. The guns are firing, and delivering the bullets to their targets. It's the bullets themselves that are not doing what they are supposed to do.
-Chris