Wolf .223
I have over 5k through my 16s using various uppers (all Colt). Zero ammo problems. Only failures are mag (always those frickin' Orlites that I'm trying to kill - don't buy Orlites!!!) related. The stuff is underpowered and will not reliably cycle my friends LMG upper, but works 100% in my 11.5s, 14.5s, and A1 and A2 20s.
I keep hearing about extractors and have yet to break anything. Obviously, the economics argument would prevail anyway. Heck, buy a complete upper with the savings.
Actually, I very much appreciate the steel cases as range cleanup is required at one of my favorite shoots. A long-handled power-mag is a joy to use.
I have something like 20k stockpiled at the moment. I trust it far more than my own reloads. RRs are too dear these days to play games with crap ammo. Wolf is inexpensive and dirty, but it is not crap ammo.
Sam