The .378 Weatherby Magnum

By Chuck Hawks

The .378 Weatherby Magnum was introduced in 1953 as a replacement for the previous .375 Wby. Mag. The .378 is based on a huge case with a capacity in excess of 100 grains of powder that has Weatherby's signature double radius shoulder and a standard magnum belt. Despite its unusual nomenclature, the .378 uses standard .375" bullets.

Jack O'Connor once wrote a rather amusing passage about Roy Weatherby's eyes popping when he (O'Connor) first showed Roy a .416 Rigby case. Weatherby must have been impressed because his .378 and .460 Weatherby Magnums are based on what is essentially a belted version of that case. So are the later .416 Weatherby Magnum and the offbeat .30-378 Weatherby. The .378, .416, and .460 comprise the trio of heavy, dangerous game cartridges for which the big case was really intended.

The .378 was the first cartridge based on the big new case. Like all Weatherby cartridges based on this case it is "overkill." By which I mean that the previous .375 Weatherby is perfectly adequate for any purpose for which the .378 (or any other medium bore caliber) might properly be used. Likewise, while the .460 is the world's most powerful .45 caliber elephant cartridge, the smaller .458 Winchester Magnum uses the same bullets and will kill any elephant that walks. Ditto the .416 Weatherby compared to the .416 Rem. Mag. None of these outsized Weatherby calibers serve any particularly rational purpose. Of course, neither do men's ties--but I digress.

In any case there can be no argument about the .378's effectiveness as a heavy and dangerous game cartridge. And if a shooter derives confidence from the oversize case and can stand its equally oversize recoil, what harm is done? An animal can't be deader than dead.

The factory ballistics for the .378 Weatherby are impressive, to say the least. Weatherby claims a muzzle velocity (MV) of 3150 fps with a 270 grain Barnes X-Bullet and 2925 fps with a 300 grain FMJ bullet in a 26" test barrel. The muzzle energy (ME) is 5948 ft. lbs. for the 270 grain bullet and 5966 ft. lbs. for the 300 grain bullet.

The only other company loading for the .378 is A-Square. They offer 300 grain bullets at a claimed MV of 2900 fps and ME of 5602 ft. lbs.

The 270 grain Barnes X-Bullet is the flattest shooting of all .378 Weatherby loads and perhaps the best all-around bullet choice for a .378 rifle. Its velocity and energy at 100 yards are 2954 fps and 5232 ft. lbs. At 200 yards the figures are 2767 fps and 4589 ft. lbs. At 300 yards the big Barnes spitzer bullet is still traveling at 2587 fps with 4013 ft. lbs. of energy. That ought to take care of anyone's pachyderm problems.

Weatherby claims that the trajectory of that load when fired from a scoped rifle zeroed at 200 yards is as follows: +1.2" at 100 yards, 0 at 200 yards, and -5.8" at 300 yards. This is a very flat trajectory for a medium bore (or any) rifle.

Handloads within about 15-100 fps of the velocities claimed by Weatherby are possible. There is a good selection of .375" bullets for the reloader. The most common sizes are 235, 250-260, 270, 285, and 300 grains. Controlled expansion bullets like the A-Frame Dead Tough, Barnes X-bullet, Nosler Partition, Speer Grand Slam, Swift A-Frame, and Woodleigh Weldcore would seem to be good all-around choices for the high velocities achieved by the .378 Mag.

According to the A-Square Handloading Manual Any Shot You Want their Monolithic Solid bullet can be driven to a MV of 2752 fps by 106.0 grains of RL22 powder, and a MV of 2911 fps by 110.0 grains of RL22. The latter load had an average pressure of 61,000 psi. These loads used A-Square cases and CCI primers, and were tested in a 26" barrel.

The big bugaboo of the .378 Weatherby Magnum is its outsized recoil. The Hodgdon Data Manual No. 26 describes it as, " . . . far too vicious for all but the most seasoned shooters." The Barnes Reloading Manual No. 1 reads, "This cartridge will develop literally tons of energy, but it is also known as perhaps the hardest kicking round there is."

The figures on my Rifle Recoil chart show that a Weatherby Mark V rifle weighing 10.5 pounds complete with scope and mount comes back at the shooter with about 58.4 ft. lbs. of recoil energy when shooting a 270 grain bullet at 3150 fps, and 58.8 ft. lbs. when shooting a 300 grain bullet at 2900 fps. Of all the shoulder arms on the chart, these values are exceeded only by the .416 Weatherby, .470 NE, and .460 Weatherby.

To conclude, I would like to quote Weatherby's rationale for the .378 Mag. from The Weatherby Guide, 19th Edition (1977):

"Because there was a definite need for a large bore, heavy bullet traveling at high velocity, we developed the .378 Magnum. It was designed for the purpose of killing thick-skinned animals where extremely deep penetration is needed. This is truly the rifle for the man who wants the utmost in killing power when concentrating on the world's largest and most dangerous game."

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Copyright 2002, 2010 by Chuck Hawks. All rights reserved.