You should read the link that I posted, because the guy that took the infamous "it'll chew up your feed ramps" pics explains they were taken totally out of context and not actual M4 uppers / and M4 cut feed ramps. Another posters ODA has been using USGI mags and M855A1 for thousands upon thousands of rounds with no damage.
It's kinda hilarious that some dude saw some pics on ARFCOM, over reacted, put out bad info, and it was never corrected. Thanks 82nd Airborne!