A/C/C's are built to a higher straightness tolerance than the FMJ's. FMJ's are a heavier shaft (grain per inch). A/C/C's are quieter across most rest that I've found. FMJ's pull from a 3D target easier. Personally though, the big kicker for me is that I hate the FMJ diamond plate finish! A/C/C's for me. One thing to be careful of with both, if you're making the switch from pure carbon, is that they can be bent. Check them now and again.