While some at Springfield, Inc. (the commercial firm, not to be confused with the US Government's now-closed original Springfield Armory) say that the M14 flash suppressor "does affect harmonics of the M1A most favorably." This is contrary to all my experience, which indicates that the flash suppressor does nothing for accuracy. It does change impact (whether on or off), but does not affect accuracy.
It should not be confused with the Browning/USRA (Winchester) BOSS system, an adjustable mechanism that does create better or worse groups. Beyond that, I am not qualified to discuss.The M14 flash suppressor, properly installed, yields NO affects on accuracy. And, of course, it is not adjustable to enable it to "affect harmonics of the M1A most favorably", even if it did have a measurable affect.
Surely, we will not believe that any old flash suppressor, installed on any old M1A will be "most favorable" for any given M14 type rifle?
I, for one, cannot propagate such broad strokes.