7mm Weatherby Magnum Ammo is a powerful 7mm rifle cartridge offered by the Weatherby firearms company in their Mark V rifles. The cartridge was one of the first cartridges offered by the Weatherby company. It was developed among the first line of Weatherby cartridges back in the early 1940s by Roy Weatherby. As other Weatherby Magnum cartridges, the 7mm Wby Mag design is based on the .300 Holland & Holland Magnum case, necked down to .284 caliber, featuring a double radious neck and a straight taper, shortened to be feed from a standard length action, as the .257 Wby Mag and the .270 Wby Mag do.
7mm Weatherby Magnum Ammo is a very adequate cartridge for hunting medium to large-sized deer such as mule deer, wapiti and moose, up to long ranges due to its plain trajectory with bullets of different weights and due to the high ballistic coefficient the 7mm bullets are praised for. However, with adequately constructed bullets, the 7mm Wby Mag may be used for hunting larger game, including the great bears and the American bison.
As with other belted magnum cartridges, recoil is significant, and due to the high pressures that are characteristic of Weatherby Magnum, recoil may be felt slight, though not as heavy as larger-caliber magnums such as the .300 Weatherby Magnum. Care must be taken to confirm what twist rate was used, as the earlier West German 7mm Weatherbys used a 1-in-12 twist vs the faster 1-in-10 twist for those of later manufacture. The 1×12 twist rifles will not stabilize bullets over 150 grains, while the 1×10 twist rifles will stabilize bullets weighing up to 175 grains.