Thoughts on the matter are a little further down the page in the thread "223 HPBT Reliability"

I would summarize my experience with 223 again, but would run the risk of being called a troll by fellas with differing opinions, so I'll just let you read them there.

As far as ammo goes, I've been fine with 75 and 69 grain HP, in whichever brand you shoot tightest, but know guys who use 55 with no noticeable difference.