The 7mm Weatherby Magnum
By Chuck Hawks
Weatherby's Big 7 is based a shortened .300 H&H Magnum case with the usual double radius Weatherby shoulder. This is the same basic case used for the .270 Wby. Mag. and .257 Wby. Mag. It is not the case used for the .300 Wby. Magnum, which is based on an "improved" full length .300 H&H case.
Factory loaded ammunition is available from Federal, Hornady, Weatherby, and Norma of Sweden (who also loads Weatherby brand ammunition). Federal offers three different bullets, all of 160 grain weight. Hornady offers their 154 grain and 175 grain bullets in their factory loads, and Weatherby offers 139, 140, 150, 154, 160, and 175 grain bullets. This might represent an embarrassment of riches, as there is not much that cannot be handled by a good 150 to 160 grain bullet in any 7mm Magnum caliber.
The Hornady factory load using a 154 grain Interlock bullet starts with a MV of 3200 fps and a ME of 3501 ft. lbs. At 300 yards that bullet is traveling at 2546 fps with 2216 ft. lbs. of energy. This same bullet is also available in Weatherby brand ammunition (at a MV of 3260 fps). This is perhaps the best bullet for game of less than about 350 pounds in the caliber, without seriously compromising performance should one get a chance at a substantially larger animal like an elk.
The Federal factory load using a 160 grain Nosler Partition bullet starts at 3050 fps with 3305 ft. lbs. of ME. At 300 yards it is traveling at 2470 fps and carrying 2165 ft. lbs. of energy. The 7mm Wby. remains about a 350 yard elk, kudu, eland, and moose cartridge. This is probably the best factory loaded bullet for really big or dangerous animals, and it is offered in Weatherby brand ammunition (at a MV of 3200 fps) as well as by Federal.
The handloader has a greater selection of bullet weights and styles, ranging from about 100-175 grains, but bullets from 139-175 grains are most appropriate in the 7mm Wby. Mag. Good reloads can about equal the velocity of the factory loads above, but not appreciably exceed them.
Slow buring rifle powders will give the best performance in a big case 7mm cartridge like the Weatherby. Reasonable choices include H1000, H4831, IMR 4831, IMR 7828, RL-22 and RL-25.
Here are some specifications of interest to handloaders: maximum COL 3.36", maximum case length 2.549", SAAMI maximum mean pressure 65,000 psi.
The sixth edition of the Hornady Handbook of Cartridge Reloading shows that their 154 grain spire point bullet can be driven to a MV of 2800 fps by 65.0 grains of RL-22 powder, and a MV of 3300 fps by a maximum load of 75.8 grains of RL-22.
The same source shows that the heavy Hornady 175 grain bullets can be driven to a MV of 2600 fps by 58.9 grains of RL-22 powder, and to a MV of 3100 fps by a maxmum load of 71.8 grains of RL-22. These Hornady loads used Remington cases and Rem. 9 1/2 primers and were developed in a 26" Weatherby rifle barrel.
The 7mm Wby. Mag. is an outstanding cartridge. There is really no reason for anyone considering a 7mm Magnum, or who needs an extremely capable all-around rifle and happens to admire Weatherbys, to refrain from purchasing a Mark V in 7mm Weatherby Magnum caliber.
Note: A full length article about the 7mm Wby. Mag. can be found on the Rifle Cartridge Page.
Copyright 2004, 2013 by Chuck Hawks. All rights reserved.