It does not really matter what attachment you use, it comes down to what suits your style of play, but with certain attachments, you will have to adapt the other parts of your overall class to make sure you get the best qualities from the gun itself. For example, using a silencer will lower the amount of power so it is important that you have Stopping Power on if you plan to use this attachment (although I would use Stopping Power anyway). I am a regular user of the ACR and I normally use the Red Dot Sight attachment for higher accuracy, but I switch to FMJ too for extra power when shooting through things, if you're intending to aim for Extended Mags. It really is up to you. Red Dot Sight is my recommendation.
a red dot sight
no way to answer without knowing what your metrics are.
The ACR or the AK-47 they are excellent
get to level 48 and you unlock the ACR
The SCAR is stronger than the ACR.
ACR means Adaptive Combat Rifle.
Unlock all the weapon attachments for the ACR. Or, if you are prestiged, get at least 500 kills or 250 headshots with the ACR.
ACR is an abbreviation for the American College of Radiography.
UMP 45. M4A1. ACR 6.8 G36. Srtiker. MSR. MP7
What do you mean by ACR? Bushmaster ACR- Many, an ACR (formerly Masada) can be configured in many barrel lengths and stock options. ACR as in 1990's rifle program- Almost every main country had a new advanced rifle concept to replace their current rifles.
Achieve the ACR Mastery Challenge.
You can attach a grenade launcher to an ACR.... if they ever enter production.