I suspect most guys here will chime in and say, "the same thing I run through my AR".
Guys, I have an NEA-15 carbine too, but, last time I checked, it's an AR. Yes, she'll take 5.56 & .223, and most of the time it's 55 grain.
What we really all want to know/see, is who's done any long distance shooting with heavier bullets, as what sets the NEA-15 apart from a lot of other stuff is the 1 in 7" twist they're using.
Let's see some results with handloads. I'm curious how the 14.5" barrels are treating the 75-77 grain loads out past 300.