Nosler's 250 Savage data showing 35 gr. H4895 and a 100 gr. Ballistic Tip at 2952 fps is right on the money out of my 24" barreled 700 Classic.
To assess the potential of the 257 Roberts one may look to 6mm Rem. loads. The 6 Rem data for 95/100 grain bullets is chock full of combinations showing 3150 fps +/-. Being possessed of the same capacity and a larger bore than the 6 Rem, the 257 Roberts will be capable of even a bit more speed when loaded to like pressure.
