My 6.5 160gr. Hornady RNs are .263" to .2635" & they shoot well from my 6.5x55 and my Daughter's .260 Rem.
Also, shooting REALLY well in my Daughter's .260, are Sierra 160gr. Semi-round nose which measure .2625". These have a VERY long bearing surface and must be seated deeply. The long bearing surface allows or even promotes them to obturate nicely.