As of now I'm thinking either .223 or .204. I singled out surplus as I am out to shoot well 90% of the time, and will buy more expensive ammo over cheap because I want better groups. I can shoot to the near limits of both my guns (Not trying for 400 yrd luck shots with my .22, but I have made them up to 300 on 14 inch gongs), so I think my ammo needs to reflect it.
I love the .243 caliber, but burnout would occur too early.
I noticed the pistol caliber idea pop up a few times, any pistol caliber rifles that are sub moa, or are they mostly fun guns or ranch carbines?