Ironic you posted this. I was just talking Davis Shorthorns yesterday about looking for me a .257 Weatherby Mark V. They're expensive to shoot - a quality round will run you >$75/box.
"Weatherby currently list five loadings for the .257 featuring Hornady, Nosler and Barnes projectiles. The light 87grain Hornady SP at 3825fps is intended strictly for varmints while the 100 grain Interlock at 3602fps and 117 grain RNSP Interlock at 3305 are both intended for use on lighter medium game. Generally speaking, the Hornady offerings are somewhat too soft for the .257 Weatherby and prone to suffer bullet blow up at close ranges but not in a spectacular killing fashion.
Weatherby’s Nosler loadings feature the 110 grain Accubond at 3460fps, the 115 grain Ballistic Tip at 3400fps and the 120 grain Partition at 3305fps. All three are loads are very useful, the BT is dynamite on lighter game weighing less than 60kg (130lb) out to moderate ranges. The Accubond is an excellent all rounder for all medium game up to 180kg out to and beyond 350 yards while the Partition is absolutely brilliant at longer ranges, regardless of its lead tip and flat base which seem antiquated in comparison to the newer Accubond.
The stoutest .257 load is the 100 grain Barnes TSX at 3570fps. This is a good muzzle velocity for the Barnes because at lower impact velocities of 3100fps and below, this projectile tends to be slow killer. The TSX is best reserved for larger deer species and especially Boar, all of which offer a great deal of resistance to the TSX."