Despite my belief in Lapua, Ian and Gord offer good advice, as guns defintely vary as to what they shoot. Just received a report from a friend to whom I loaned a nice Sako M591with mew Gaillard barrel and it doesn't shoot 154 grain .30 Lapua bullets. Haven't tried other 155 bullets. A newer .308 shooter is getting .2 -.3 MOA with the same bullets, but he has a CIP spec reamer and perhaps that's the way to go, but this a little OT.
Regards,
Peter