At the risk of starting a flame war, Clay Harvey's book Rifle Cartridges doesn't list the Roberts with a whole lot of favor. He speaks of the cartridge as not being as accurate as many other choices. Those are his words, not mine. I'm sure someone else will chime with claims of 1/2" groups at 300 yards. We've all got our opinions.

I only have extended experience with one .257 Roberts. It's a Ruger 77 that we've never been able to coax much better than 2" groups at 100 yards out of. As far as performance on whitetails, it's taken 8 or 10 deer so far though. My cousin hunts with it and he's more than happy with the performance.