The .240 Weatherby Magnum
By Chuck Hawks
The .240 Weatherby Magnum was introduced in 1968, and it was the last Weatherby caliber introduced while Roy Weatherby was alive. The .240 Weatherby case is unique. It is a standard length and diameter cartridge with a .473" rim diameter, the same as a 30-06, and it will work through any standard length action. Like all Weatherby cartridges, it is a belted case with a double radius shoulder. It is a very cute magnum cartridge, with a powder capacity much like that of the 6mm-06 or 6mm-284 wildcats. Norma manufactures Weatherby brand ammunition. The .240 has a SAAMI maximum average pressure of 53,500 cup.
The .240 Weatherby is the highest velocity commercially produced 6mm cartridge. It will drive a 100 grain bullet about 150 fps faster than the 6mm Remington or .243 WSSM from a 26" barrel, less from a 24" barrel. Of course, if the 6mm is measured in a 24" barrel and the .240 in a 26" barrel, which is the case with factory load ballistics, the difference goes up to about 300 fps.
.240 Weatherby factory ammunition is offered only by Weatherby. Bullet weights of 87, 90, 95, and 100 grains are currently offered. The .240 case is unique and cannot be formed from any other existing case, which has somewhat limited the cartridge's popularity with reloaders.
Current Weatherby figures claim a muzzle velocity of 3406 fps for a 100 grain spitzer bullet from a 26" test barrel. At 100 yards the velocity is given as 3136 fps and the energy as 2183 ft. lbs. And at 400 yards the velocity is still 2415 fps and the remaining energy an impressive 1294 ft. lbs.
The trajectory of that load (using a Nosler Partition bullet) is as follows: +2.8" at 100 yards, +3.5" at 200 yards, 0 at 300 yards, and -8.4" at 400 yards. That will do for deer to about 350 yards, and qualifies the .240 Weatherby as a true ultra-long range rifle.
Handloaders have a huge selection of bullets from which to choose, since the .240 Weatherby uses regular 6mm bullets. Bullet weights range from 55-115 grains. But the most popular bullets are those weighing from 70 to 105 grains.
For hunting weight bullets, slow burning rifle powders are most efficient in the .240 Mag. H4831, H450, IMR 4831, AA 3100, W760, and RL-22 are reasonable choices.
Here are some specifications of interest to .240 reloaders: bullet diameter .243", maximum COL 3.10", maximum case length 2.50", MAP 53,500 cup.
I took the following two loads from the Speer Reloading Manual No. 13. The good folks at Speer chronographed their loads in a Weatherby Mark V hunting rifle with a 24" barrel, using Weatherby brass and CCI 250 primers.
With the Speer 80 grain varmint bullet in front of 50.0 grains of IMR 4831 powder the MV was 3327 fps. In front of 54.0 grains of IMR 4831 the velocity rose to 3583 fps.
Using a 100-105 grain Speer bullet and 45.0 grains of W760 powder the MV was 2922 fps. A maximum charge of 49.0 grains of W760 gave the same bullets a MV of 3206 fps.
The fifth edition of the Nosler Reloading Guide shows that with their 95-100 grain bullets 49.0 grains of RL-22 powder achieves a MV of 3082 fps. A maximum load of 53.0 grains of RL-22 can drive the same bullets to a MV of 3352 fps. Weatherby cases and Federal 210M primers were used in these loads, which were chronographed in a 24" Weatherby barrel.
Note: A full length article about the .240 Wby. Mag. can be found on the Rifle Cartridge Page.
Copyright 2004 by Chuck Hawks. All rights reserved.