Will be curious what you do with it, there's not much powder in there. I like 8.6 blackout, have a few of those, but my understanding is that Hornady didn't like the fast 1:3 twist as it sheds the petals on many of the Barnes bullets, but I don't think it does on their CX, they seem to believe the twist is not a problem to be less aggressive, so the bullets don't fragment on impact. I ponder if 6.5 Grendel isn't better suited in the mini-action, there sure isn't very much powder to play with. Only, they don't do subs. I would take 300 blackout over 338 ARC, at this point, or 6.5 Grendel, both of which I have now. And 8.6 blackout with a 285-300 grain bullet is spinning like a blender on impact...but those 210 TTSXs look pretty wicked...
What's your attraction to 338 ARC? (aside from fitting in an AR-15)