The 257 Roberts is an excellent cartridge. I believe it needs to be a handloaded round to get the most out of it, as it is none too popular any more, so the factories don't do it justice. Another good one is the 6.5X57, almost the same, but with heavier bullets. The .260 Remington and the 6.5X55 would also be good choices. The 6.5mm 140-grain bullets have excellent ballistic properties.