.260AI has no factory headstamped brass. But is a great choice, and you can still shoot .260 Rem ammo in a pinch.
6.5x47L is a fantastic round, but there are others that are faster to extend ranges.
I am no supporter of the 6.5 CM either. Too mainstream for me.
6.5x55 Swede (or an AI version)
6.5-.284 Win (or Norma) gets you better speed yet
.264WM, but with a short barrel, probably not the best choice.
6.5 SS or 6.5 SST (no factory headstamped brass, but these cartridges are amazing)
What about a fast twist hot 6mm? Run from 55 to 117 grain bullets.
.243 Win
6mm Rem
6x47L
6x47 Swiss Match
6XC
6 Dasher
6 PPC
.243 WSSM