Rel-19 works very well in 6.5x55 as does Rel-22, IMR4350, H-4350 for starters. Basically any of the medium-slow burning powders work in 243 & 6.5x55. Check your local manuals. Specific loads from other people doesn't mean that it will shoot well in your own rifle. Look at Hodgden.com or Alliantpowder.com for recommended loads. They are both excellent and capable cartridges.
NCsmitty