.257 Weatherby Magnum

The .257 Weatherby Magnum is a .25 Caliber (6.35 mm) belted bottlenecked cartridge. It is one of the original standard length magnums developed by shortening the .375 H&H Magnum case to approx. 2.5 in (64 mm). Of the cartridges developed by Roy Weatherby, the .257 Weatherby Magnum was known to have been his favorite, and the cartridge currently ranks third in Weatherby cartridge sales, after the .30-378 Weatherby Magnum and the .300 Weatherby Magnum.

The .257 Weatherby Magnum is among one of the flattest shooting commercial cartridges. It is capable of firing a 115 gr (7.5 g) Nosler Ballistic Tip bullet at 3,400. ft/s (1,036 m/s) generating 2,952 ft·lbf (4,002 J) of energy which is comparable to factory loadings of the .30-06 Springfield and the .35 Whelen in terms of energy.

Discrepancies between the metric and U.S. diameters of the bullet may cause some confusion. A .257 bullet has a metric bullet diameter of 6.53 mm. However, in Europe cartridge designation nomenclature for a large part relies on the bore diameter. As the bore diameter of the rifle is .250 inches this would make the .257 Weatherby Magnum a 6.35 mm caliber cartridge rather than a 6.5mm caliber cartridge.