The .257 Weatherby Magnum dates back to 1943, when Roy Weatherby began experimenting with the .300/.375 H&H Magnum case for a series of wildcat cartridges, most of which later became proprietary and today are SAAMI standardized. By blowing out the belted case, giving it minimal body taper, then adding a unique double-radius shoulder, shortening it to 2.549 inch and necking it to accept .257-inch bullets, the .257 Weatherby Magnum was born. Using 115- to 120-grain bullets, velocities hovered between 3,300 and 3,400 fps, while 100-grain bullets reached over 3,600 fps. The result is an extremely flat shooting cartridge that produces comparatively mild recoil and is excellent choice for hunting deer and antelope in open country. When loaded with premium big game bullets it is suitable for larger game such as elk and African plains game. When handloaded with lightweight bullets, such as the Sierra 75-grain HP, the .257 Weatherby can crowd 4,000 fps to produce spectacular results on varmints such as rock chucks, coyotes, etc.

The test rifle used here, a Weatherby Mark V (Japan manufacture), proved capable of groups that measured well under one inch, but experimentation with bullets seating depth was required.

Avoid reducing loads below the suggested “start” charges, as erratic velocities and pressures can occur, which is especially true with spherical (or ball) powders. None of the loads here exceed industry maximum average pressure guidelines that were established in 1994 at 53,500 CUP.