I have a .223 Ultra, that I have determined was produced in '04, S.N. NU 252XXX. Can anyone help me with the twist rate. Second, what is the rule of thumb for twist rate and bullet weight as far as accuracy. Is it 1x9 and lighter bullet or heavier bullet. 1x12 in lighter or heavier bullet. I don't reload so I'm trying to determine where to start with factory loads to acheive the best accuracy. Thanks!!