Sure Shot, 6.5mm/26caliber cartridges have a long track record of excellent accuracy in competitive shooting disciplines. 27 caliber cartridges do not. But that's 'cause good match bullets have been made in 26 caliber for decades whereas 27 caliber ones have not.
Had the .308 Win case been necked down to 27 caliber and Sierra made three weights of good match bullets some years ago, the .270-.308 wildcat may well have been the round to go with instead of the 7mm-08.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master