You can use a hornady seater with the sliding sleave, just get one for a 6.5mm (260 Rem or 6.5 Rem mag) the sleeve drops down over the neck keeping the case and bullet straight. I use the same ones for my 5.6x50R and 22-250, 6mm-204 and 243 also the 25-204 and 250 Savage.
As Erich says, I use Hornady seaters on many different cartridges.
As Greydog says, there is really no reason to harden a seater.
