I have a full custom Nesika 6ppc short range benchrest rifle that I love, but don't use that much as I currently enjoy LR shooting more. I am considering having another barrel spun up, but am a bit limited by that bolt face. I happen to have AR uppers in 6mmAR and 6.5grendel so i'm all set up with dies and brass for those two cartridges so those two would be an easy conversion. At most I would use it in an informal 600 yard benchrest match, but mostly just trying to shoot small groups at 600 yards. Would you choose 6mmAR or 6.5grendel for this purpose? Or is there another cartridge that would be worth buying dies and brass for? Any advice on bullet weights to choose/advice based on experience with this sort of thing? Thanks in advance.