.338-378 Weatherby Magnum

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.338-378 Weatherby Magnum
338-378 Weatherby
Type	Centerfire/Rifle
Place of origin	United States
Production history
Designer	Elmer Keith and Bob Thomson
Designed	1963
Manufacturer	Weatherby
Produced	1998
Specifications
Parent case	.378 Weatherby Magnum
Case type	Belted, bottleneck
Bullet diameter	.338 in (8.6 mm)
Neck diameter	.361 in (9.2 mm)
Shoulder diameter	.560 in (14.2 mm)
Base diameter	.582 in (14.8 mm)
Rim diameter	.579 in (14.7 mm)
Rim thickness	.059 in (1.5 mm)
Case length	2.905 in (73.8 mm)
Overall length	3.65 in (93 mm)
Case capacity	125 gr H2O (8.1 cm3)
Rifling twist	1 in 10
Primer type	Magnum Rifle
Maximum pressure	63,817 psi (440.00 MPa)
Ballistic performance
Bullet mass/type Velocity Energy 250 gr (16 g) Partition type 3,060 ft/s (930 m/s) 5,197 ft⋅lbf (7,046 J) 225 gr (15 g) Truncated solid 3,180 ft/s (970 m/s) 5,052 ft⋅lbf (6,850 J) 200 gr (13 g) Boat-tail soft point 3,350 ft/s (1,020 m/s) 4,983 ft⋅lbf (6,756 J)
Test barrel length: 28 in (71 cm) Source(s): Weatherby [1]

The .338-378 Weatherby Magnum is based on the .338-378 KT, a wildcat cartridge created by Elmer Keith and R.W. "Bob" Thomson in 1966.^[2] The KT is based on the .378 Weatherby Magnum cartridge but is shorter by 1/4" and necked down to a .338 caliber bullet.^[3] This design was chosen for elk hunting, using the powders available at the time, such as Hodgdon H-4831.^[4] Due to the continued popularity of the KT, Weatherby introduced the .338-378 Weatherby Magnum in 1998 to its line of commercial ammunition, using a full-length 2.908" case.^[3] Although based on the .338-378 KT, the .338-378 Weatherby Magnum and the KT have different load data and chamber sizes and are not interchangeable.^[5]