The authors of this report took 4 identical Bushmaster MOE rifles and fed them each a different brand of ammo for 10k rounds to note changes in wear and tear. The whole report is an excellent read; but some of the more interesting points to me were:
1. Russian ammo does cause additional wear - not so much from the steel cases but from the bimetal jackets. Barrels shot out roughly twice as fast and reliability worsened earlier.
2. An excellent example of how a midlength functions to take ammo that was marginal in a carbine and shoot it reliably from the midlength.
3. Those cheap components that look just like what comes in a Colt but cost half as much? They matter and affect reliability.
Great read and well worth your time.