RE: .257 roberts
I achieved over 2900 fps with a Hornady 117 gr. BTSP with 49.0 gr. H4831, Winchester brass, & Federal 210 primer. The gun was a Remington 700 Classic Stainless with a 22" barrel. This produced 1/2" three shot groups. I also used RL19 but did not reach the velocity I wanted before seeing pressure signs.