Too much torque on the muzzle device is not good for accuracy.
My suppressors are on just a little past "hand tight", as I like to remove them without a lot of effort when testing ammo. Ammo that is, that is inherently accurate enough (i.e., 2 moa or less). to show any differences.
Problem with issue A2 Flash Suppressors (that cost the gov about $3.00 or less each)is that they are not exactly round, nor is the hole down the middle round, i.e., "the bore", and the bore is probably not concentric, i.e., lined-up perfect with the rifled bore, either.
Solution to this situation is:
(1) buy a vortex if a "non-issue" device is acceptable.
(2) if you must have the "issue look" buy one of our (I work at KAC) M4 "QD" Flash Suppressors, but these cost $50.00+.
(3) or the first thing you should try is: bore out your flash suppressor until you no longer see any difference in accuracy. This is what we used to do with Match M14 Rifles that had to have the "issue" flash suppressor.
ColdBlue sends...