.378 Weatherby Magnum

The .378 Weatherby Magnum was designed by Roy Weatherby in 1953.[3][4] It was an original belted magnum design with no parent case, inspired by the .416 Rigby and headspacing of the belted .375 H&H Magnum.[5] The 215 magnum rifle primer was developed by Federal specifically for this round.[5] The cartridge can hold upwards of 7.13 g (120 gr) of powder. The 378 Weatherby Magnum cartridge also has the double radius shoulder design found on the first and smaller proprietary line of Weatherby magnum cartridges.

.378 Weatherby Magnum
.378 Weatherby Magnum, center
Type	Rifle
Place of origin	South Gate, California
Production history
Designer	Roy Weatherby
Designed	1953
Manufacturer	Weatherby
Produced	1953-Present
Specifications
Case type	Belted, bottleneck
Bullet diameter	.375 in (9.5 mm)
Neck diameter	.399 in (10.1 mm)
Shoulder diameter	.560 in (14.2 mm)
Base diameter	.582 in (14.8 mm)
Rim diameter	.579 in (14.7 mm)
Rim thickness	.063 in (1.6 mm)
Case length	2.913 in (74.0 mm)
Overall length	3.65 in (93 mm)
Rifling twist	1 in 12 in (300 mm)
Primer type	Large rifle magnum
Ballistic performance
Bullet mass/type Velocity Energy 300 gr (19 g) Full Metal Jacket 2,925 ft/s (892 m/s) 5,699 ft⋅lbf (7,727 J) 300 gr (19 g) Round nose 2,925 ft/s (892 m/s) 5,699 ft⋅lbf (7,727 J) 270 gr (17 g) Truncated solid 3,060 ft/s (930 m/s) 5,613 ft⋅lbf (7,610 J) 270 gr (17 g) Pointed soft point 3,180 ft/s (970 m/s) 6,062 ft⋅lbf (8,219 J) 260 gr (17 g) Partition Type 3,140 ft/s (960 m/s) 5,743 ft⋅lbf (7,786 J)
Test barrel length: 26 in (66 cm) Source(s): Weatherby [1] / Nosler [2]

The motivation behind the development of the .378 came from the disappointing performance gains of the improved .375 Weatherby Magnum over its parent case, the .375 H&H Magnum.[6][7] Roy Weatherby in 1953 killed an African elephant with one shot while on safari. However, in using this event as a marketing tool, it was revealed some African countries have a minimum 10.16 mm (.40 caliber) bullet size for hunting dangerous game.[5] Weatherby responded by necking up the .378 to 11.63 mm (.458 caliber) and called the new cartridge the .460 Weatherby Magnum, which was introduced in 1958.[8]

Considered a safari-grade cartridge, the .378 Weatherby Magnum is appropriate for taking all African game animals from large African antelopes, Nile crocodile, hippopotamus, to the Big Five game. Some hunters on the North American continent employ the .378 for American elk, brown bears, and polar bear.

The .378 Weatherby will generate considerable free recoil, an average of 104 J (77 ft·lbf) from a 4.1 kg (9 lb) rifle. This compares to 27 J (20 ft·lbf) from a rifle chambered for .30-06 Springfield or 49 J (36 ft·lbf) for the .375 H&H Magnum.[9] The traditional stock used on the Weatherby Mark V tends to accentuate felt recoil.[10]

The .378 has been responsible for numerous wildcat cartridges, being necked-down as the .22 Eargesplitten Loudenboomer and necked-up as the .500 A-Square.[11][12] Some of the .378 Weatherby Magnum wildcat cartridges are shortened versions, like the .30-378 Arch (7.62 mm) and the .460 Short A-Square (11.63 mm).[13][14] Some .378-based wildcats have gone on to be part of the Weatherby line: .30-378, .338-378, .416 and .460.[15] In addition, the .378 WM is used as the parent case for the .460 Weatherby Magnum.[16]