As long as the rim is okay and the brass has no neck splits you should be okay.
I'm not sure how M4/M16s are on brass, but M249s can leave quite a ding in the rim from the powerful hit against the ejector.
I bought a bunch of brass that was fired in a M249, and about 1% of it was not useable.
There is no difference in the brass between 5.56 and .223. They are both identical. I have seen a .223 with a 5.56 reamer run in it, and the only thing that came out was a little of the phosphate coating right at the neck, and there's no evidence that isn't the difference that another .223 reamer would also take out, or another 5.56 reamer wouldn't touch.
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