TG,
I use 160 grain Sierra Gamekings with Vit N165, Remmy magnum primers and Winchester brass. My barrel length is 26 inches.
Brass choices for the 7mm RM are a bit limited in the UK compared to other cartridges. I use Winchester almost by default. The stuff I've had was not great to look at straight from the bag. The necks were rough and needed sizing to shape and trimming to length. I didn't get into weighing them so don't know how consistant they are.
However, with some initial case prep carried out, the Winchester brass has produced accuracy beyond my capabilities, so am happy with it.
When I first got my Rem Mag I was advised to run bullets at the heavier end of the spectrum for UK deer. I think that's sound advice. I've had good results and minimal damage from the 160 grainers.
Cheers,
Bob