240 Weatherby Magnum

In 1968, Roy Weatherby added this 6mm chambering to his line of belted magnums. As with other Weatherby cartridges, this number was designed to generate significantly more velocity than any existing commercial 6mm chambering.

However, there is not much new under the sun. The 240 Weatherby is ballistically very similar to the, then, 45-year-old 244 H&H Belted Express, which was originally designed by necking down the 375 H&H case. While, in that earlier era, designers of the 244 H&H did not have the slow propellants necessary to develop respectable ballistics, Weatherby could take advantage of newer, slower burning powders. Today, even better slow-burning propellants are available, modern 240 Weatherby performance reflects this fact.

The 240 Weatherby case is unique. It is essentially a 30-06 case with the body swaged down to create the trademark Weatherby belt. Capacity is very similar to the 30-06 and near the top of what can be generated in a 6mm bore with anything resembling reasonable barrel life. Given a 26-inch barrel, it will out-distance 243 performance by 300 to 400 fps, which accounts for an impressively flat trajectory.

Barrel life can be an issue, particularly with infrequent cleaning or when one shoots too many shots without allowing significant time for cooling, like at a good varmint hunting. As a big game chambering, the 240 WM is useful for the same purposes as the 243 and adds at least 100 yards of useful range, compared to that popular number.