The .30-378 Weatherby Magnum

By Chuck Hawks

In recent years there has been a trend among wildcat cartridge aficionados toward outsized "super" .300 magnums. In 1996 Weatherby responded to this trend by chambering their Mark V rifle for the huge .30-378 Belted Magnum. But the .30-378 really dates from the 1950's when Roy Weatherby developed it at the request of the U.S. government as part of their research into ultra-high velocity rifles. This is the most over the top .30 cartridge ever introduced by a major rifle manufacturer.

The Weatherby .30-378 Magnum is based on the belted .378 Wby. Mag. case necked down to .30 caliber. The case looks much like a belted version of the .416 Rigby case, on which the .378 was based. It is spectacular in every dimension. The rim diameter of the .30-378 case is .580" and the diameter at the belt is .604". At the base of the shoulder the case measures .561" in diameter, and the case length is 2.908". Naturally, the .30-378 uses Weatherby's usual double radius shoulder design, and accepts standard .308" diameter bullets. The overall cartridge length is 3.648".

Unlike the .300 Ultra Mag, the .30-378 Weatherby has a full diameter rim for maximum feeding reliability from the box magazines of bolt action rifles. It is suitable for use on thin-skinned dangerous game of the largest sort, such as lion, tiger, grizzly, brown, and polar bears.

Weatherby Mark V rifles for this caliber weigh about 8.5 pounds (empty and without a scope or sling) and have 28" barrels. Needless to say, a bolt action rifle with a 28" barrel is not a real handy weapon, but the long barrel and substantial weight is a practical necessity for a rifle of this power. Even in a scoped, fully loaded, Mark V rifle weighing 9.75 pounds the 180 grain factory load for the .30-378 punishes the shooter with some 51.4 ft. lbs. of recoil energy.

Weatherby factory ballistics for the .30-378 call for a 165 grain bullet (SD .248) at a MV of 3500 fps with ME of 4488 ft. lbs., a 180 grain bullet (SD .271) at a MV of 3,420 fps with ME of 4676 ft. lbs., and a 200 grain bullet (SD .301) at a MV of 3,160 fps with ME of 4434 ft. lbs. Weatherby ballistics tables show the following trajectory for the 180 grain Nosler Ballistic Tip bullet: +2.5" at 100 yards, +3.1" at 200 yards, 0 at 300 yards, and -7.5" at 400 yards.

Even at 400 yards the remaining energy of this load is a whopping 2797 ft. lbs. For the shooter who can reliably deliver solid hits in the heart/lung area at that range (probably less than 1 in 1000 hunters), the .30-378 undeniably has the power to kill elk and moose at 400 yards.

It would seem that heavy bullets of 200 to 250 grains would be most suitable for such an outsize case, but no bullets over 200 grains are available in factory loads. However, the reloader has access to the various 220 grain bullets (SD .331), and the super heavy Barnes 250 grain Original bullet (SD .376).

Hodgdon Powder Company reloading data shows that a 180 grain Speer boat-tail spitzer bullet can be driven at a velocity of 3213 fps by 105.0 grains of H870 powder, and to a MV of 3412 fps by 111.0 grains of H1000. The 200 grain Barnes X-Bullet tested by Hodgdon could be driven to a MV of 3105 fps by 113.0 grains of H870 powder, and to 3206 fps by 116.0 grains of H870.

Last but certainly not least, the 220 grain Nosler Partition bullet could be driven to a MV of 3098 fps by 113.0 grains of H870 powder, and a MV of 3180 fps by 116.0 grains of H870. With a well placed bullet this should do for any animal on earth, although no .30 caliber cartridge it really the best choice for heavy, dangerous game. These velocities were all achieved in a 26" barrel and used Weatherby brass and Federal 215M primers.

Case life and barrel life are expected to be short for the .30-378 because of the high velocity and the great amount of powder burned per shot. However, the .30-378 is the hardest hitting of all the popular ultra-long range rifle cartridges. That is true at both ends, of course!

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Copyright 2003, 2012 by Chuck Hawks. All rights reserved.