ACR is too weak, it has one of the weakest damage powers of the assault rifles. Without stopping power and FMJ it takes a lot of shots to kill, unless you play hardcore and one or two shots can kill.
true, it's a pretty weak weapon without those, but it's probably the best *with* those.. it doesn't matter how far away they are, you can just click your left mouse button and u'll hit with every single bullet, no recoil ftw

and once you start hitting him, he has no way to fight back anyway
because it shoots faster than most other weapons (faster than SCAR for example)
it'll make you think you die with 1-2 hits from it. (latency)