A relative of mine is shooting my SIG556xi with Manticore Arms' NightBrake, using the .223 Federal American Eagle .55 gr FMJ.
Holy crap, it's not even 5.56!!!
Got to dig out and trim the video of XM193 NATO we shot next. I'm surprised my Range card still works there (i.e. I'm still OK to go back).
Last "documentary" on this topic: it's been replaced with (my 3rd) Miculek .223 comp.