.240 Weatherby Magnum

The .240 Weatherby Magnum was developed in 1968 by Roy Weatherby. In the development of his own .240in/6 mm cartridge, Weatherby was significantly influenced by both the success and the limitations of the .244 H&H Magnum cartridge devised in England by his friend and colleague David Lloyd. It was the last cartridge to be designed by Roy Weatherby.

Design
The .240 Weatherby Mag. is a proprietary cartridge used only in Weatherby rifles. This particular Weatherby case is unique, other than shape, it isn't physically based on other Weatherby cases, having the same rim diameter and similar length as the .30-06. It utilizes the traditional Weatherby rounded double shoulder and a belted case with a length of 2.496in, significantly shorter than the 2.8in case of the .244 H&H Mag.

Performance
In terms of velocity, the .240 Weatherby is the fastest commercially produced 6 mm cartridge. There are of course several faster wildcat rounds available, but the .240 Weatherby outclasses the 6 mm Remington and the newer .243 WSSM by about 150 ft/s. While favoured by some varmint hunters, the .240 Weatherby Mag. is not much liked by some reloaders because the case cannot be formed out of any other brass; one either has to buy Weatherby ammunition or reload used Weatherby cases which tend to be more expensive than those for more common cartridges. With the heavier bullets the .240 Wby. Mag. makes for a good deer hunting cartridge, but it does tend to require a long (>23 in.) barrel in order to achieve peak performance.