I think there were a couple guys shooting AR 223's at the match I attended. Shoot what you've got. I'd gun a 69 tmk, 70 rdf, or 75 Hornady bthp in an AR platform. You'll definitely be down on horsepower at "long" range, but that shouldn't stop you from giving it a go.
I live in the upper Midwest and the matches I plan on attending are part of the Border War Rifle Series.
