Steve,
I have really nothing more to add that Mr. Shaw didn't say....
Two bullets come to mind that are typically fairly easy to get in tune, one a custom another a semi-custom...
Custom: the Bart Ultra 66gr... The 68gr Ultra a close 2nd.......... I compare the 66 Ultra to my own bullets out of an OUTSTANDING set of Larry Blackmon 6mm bullet dies.
Semi custom: Berger 65gr BT......... Shoots amazing in a wide range of barrel / chambers... I know of several 6mm BR shooters whom speak HIGHLY of this bullet from 100yds out to 600... I shot a (weep) 249 24x with this bullet a few years ago....!
There are PLENTY of FINE 6mm (60 - 70gr) bullets for = or slower 13 twist barrels... Heck, I have played around with Sierra 70gr Blitz King in 14twist BR Kreigers.... Would shoot aggs right at .250.... But not quite good enough to get below that level of accuracy...
As with REAL good barrels, REAL good bullets shoot at a high level with minimal fuss... Hummer barrels and Superman bullets are just this BUT are IMOP are at ANOTHER level...!
cale