ThisIt would be so much expense and trouble, we will likely be asking you why you don't just trade up to an AR.
When (if) you are a CURRENT army ranger you might realize that the 5.56 does exactly what it is supposed to do.
The Marines I know, and the ones I've shot with, seem to like 5.56x45mm fine. A lot of its bad rep comes from the relatively poor performance of M855 out of shorter-than-intended barrels, but even M855 works, M193 works better at realistic ranges, and the newer Mk 262 and SOST loads give very good performance by any measure.there aren't many marines that I know that have much confidence in the 5.56. Oh and one Army SF that I know seems to think they are pretty poor killers. I guess you have to be a ranger to really understand how awesome the 5.56 is. My personal opinion is that it makes sense to carry small rounds that you can fit lots of ammo into a mag but there is a trade off in lethality. Just like if you want lethality you trade capacity for it. That isn't to say that the m4 sucks cause all of these guys love the platform but not the round.