26 nosler keeps it simple and new. Add a belt and go for 6.5-300.
I necked it down to 7mm and it was successful. 160gr AB 3250fps. I used retumbo and h1000. I didnt have to anneal brass, but to go to 6.5, it might need it. You could probably cheat and do the 300prc down to 6.5.I was wondering if a 375 Ruger could be necked down since it has always intrigued me from case volume.