I have seen a light on M4's that looks like a black box (approx 3.5"x1.0"x5.0") with a light and a laser on one end. It is always on an active military weapon and not part of a manage of junk on a poser rifle. So I am pretty sure it something important, but I have no idea what it is.
If I can find a pic, I will post it.
Thanks
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