The .257 Weatherby Magnum was introduced during the mid 1940's, back when Roy was still building custom rifles around war surplus '03 Springfield and the '98 Mauser actions. It was always a favorite cartridge. The .257 Weatherby Magnum is seen at its best when burning a slow powder in a 26" barrel. A shorter barrel is handier but it cuts back on .257 Magnum performance by a substantial degree. H4831 and IMR-4831 are good choices for this cartridge when loading bullets up to 100 grains, but H870 and IMR-7828 will usually push heavier bullets faster at equal chamber pressures. Due to the extremely high velocity possible with this cartridge, bullets of controlled expansion design are best for shooting big game heavier than Whitetails and Pronghorn. The Nosler 120 grain Partition and Remington 120 grain Core Lokt are excellent bullets for shooting big game with the .257 Weatherby Magnum. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.