Starline's 6.5 Grendel brass has been good for me. I neck it down to 6mm and it seems to be good stuff.
I bought some Prvi Partizan 6mm Remington brass about 18 months ago, I guess. I cannot seat primers in it without swaging the pockets (I don't care to cut the primer pocket with a chamfer tool). I was luck enough to find the correct tool somewhere for the job...at least it was correct after a little machining.
