Hey Doug,
50 and 55gr are the standard.
I shoot 40gr, 50 and 52 in my .222 with 1:12 twist, but I don't go past 200mtrs.
Sierra MK, Speer, and Nosler Ballistic tips the best so far.
It's a rear locker, so I don't load them hot.
My .223 is a 1:12, and I shoot 55gr GameKings and Nosler Ballistic tips best out to 200mtrs.
I suspect that it would group a bit tighter with the 52gr MK's.
Might depend on how far out you want to shoot ?
A heavier bullet might be better at distance, but you must be careful of pressure, as the .222 is rated at 50,000 cpu and the .223 at 55,000, so you might have to sacrifice speed.
cheers,
Sean in 'Godzone'