What needs to be done to my bolt going from .243 to 6.5 Grendel?

[Mtnev]

If a .243 isn't enough, a 6.5 grendel won't be any better. You're reducing case capacity and increasing bullet weight. Maybe look at .260 or 7mm-08 if you think you need more.

I think the Grendel really shines in stuff like mini-mausers and Cz527's. Super-light or youth guns.