The mushrooming issues have been discussed ad infinitum. Furthermore, they are issues from the pst -- the distant past and were limited to a very small lot as discussed above. I have several of the latest model G6A2 types, and their variants to include the G6A2 5.56mm, the limited production G6A2 6.5mmG/6.8mm and the very new "Direct Connect" (DC) Vortex for use on the (EBR-14) M-14. A few versions for the M249 and M240 as well. None of these have mushroomed or shown any signs of fatigue after many, many thousands of rounds. In part, this should not be suprising since the surface hardness of the G6A2 is RC 58-60 (!) with a core hardness pushing RC 40. Tough enough for you. I know, because I saw the physical testing results at ARDEC last year.
Interestingly enough, but not entirely germane to this thread, the G6A2 M249 actually improves group size. BTW, the systemjust became available with an extremely robust BFA that works on the M-4 & M16 as well (USG only).
As an aside, I wish these forums had more in the way of technical discussions from people who use M-15-related components in their official capacity. DCD Ft. Benning used to have such a discussion board but it is no longer up. Too bad. Still, it is interesting, although frankly anecdotal to hear the observations of consumers at the retail level -- but only that. Every once in a while though, a forum contributor comes up with an observation that Force Developers/Modernizers can actually appreciate. An believe me -- they, we are listening.
When you use these items every day in real life siutations, these matters take on an entitrely different tone. Somehow commentary on how "cool" or "bad" something looks, without a critical discourse on on the technical merits is amusing at best to troops on the line.