The .375 Weatherby Magnum

By Chuck Hawks

Roy Weatherby introduced his .375 Magnum in 1945. It was based on an "improved" (that is blown-out) .375 H&H case, and uses the same .375" diameter bullets. To "fire form" a .375 Weatherby case a .375 H&H cartridge is fired in a rifle with a .375 Weatherby chamber. The brass case expands under the pressure of firing to form fit the chamber.

The result is a .375 case with much straighter walls and a (sharp) radiused Weatherby shoulder. Powder capacity is increased enough to allow handloaders to achieve about 100 fps greater muzzle velocity than with the original .375 H&H case. Factory loads for the .375 Wby. are good for about 200 fps over typical .375 H&H factory loads.

The .375 Weatherby makes a lot of sense to me. The .375 H&H Magnum is the classic medium bore cartridge, but its long tapered body and sloping shoulder were designed for the long strand Cordite smokeless powder in use in Britain during the early years of the 20th Century. Why not modify the basic .375 H&H case for optimum performance with modern smokeless powders? That is exactly what Roy Weatherby did when he designed his .375 Mag.

Like the .375 H&H, the improved .375 Weatherby is adequate for all thick-skinned big game worldwide. It is also a good choice for the great bears of North America.

In 1953 the .375 was dropped from the Weatherby line. Its place was taken by the .378 Weatherby, based on a belted version of the enormous .416 Rigby case. The .378 quickly earned a reputation as one of the nastiest kicking cartridges ever invented, but its effectiveness on all sorts of large and dangerous game is unquestioned. The .378 is, however, overkill since the .375 Wby. Mag. and earlier .375 H&H Mag. have proven more than adequate for all purposes for which a medium bore rifle is suited.

In 2001 the .375 Wby. Mag. was reinstated in the Weatherby line, probably because it appealed to hunters who were reluctant to put up with the recoil of the .378 Wby. Factory loaded ammunition is offered by Weatherby and A-Square. The A-Square loads call for a 300 grain bullet at 2700 fps.

The Weatherby factory load for the .375 drives a 300 grain Nosler Partition bullet (BC = .398) at an advertised muzzle velocity of 2800 fps with 5224 ft. lbs. of muzzle energy. The figures downrange are as follows: 2572 fps and 4408 ft. lbs. at 100 yards; 2366 fps and 3696 ft. lbs. at 200 yards; 2140 fps and 3076 ft. lbs. at 300 yards; 1963 fps and 2541 ft. lbs. at 400 yards.

Weatherby trajectory tables show a 300 yard zero with a scoped rifle with the following trajectory: +4.6" at 100 yards, +5.4" at 200 yards, 0 at 300 yards, and -13" at 400 yards. Reduce the trajectory to a more reasonable +3" at 100 yards and a spitzer bullet should hit about +4" at 200 yards and -4" at 300 yards, making the .375 Wby. a good 300 yard big game caliber.

According to the 26th edition of the Hodgdon Data Manual the reloader should expect a MV of about 2700 fps from .375 Weatherby reloads when using a 270 grain bullet. Hodgdon data shows that a 270 grain bullet can be driven to a MV of 2718 fps by 78.0 grains of H4895 powder. The Hodgdon technicians used a 26" free-bored test barrel to develop this data.

According to the A-Square Handloading Manual Any Shot You Want the reloader should expect a MV of about 2700 fps from .375 Weatherby reloads when using a 300 grain bullet. A-Square data shows that their 300 grain Dead Tough bullet can be driven to a MV of 2558 fps by 88.0 grains of RL-19 powder, and 2743 fps by 92.0 grains of RL-19. The pressure of the latter load was measured at 55,100 cup. The A-Square technicians used A-Square cases and CCI 250 primers; all testing was done in a 26" test barrel.

The recoil energy when shooting the Weatherby factory load amounts to almost 51 ft. lbs. in a 9.5 pound rifle. That is a lot, but considerably less than the recoil of the .378 Weatherby, which pretty well explains the return of the .375 Weatherby Magnum.

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Copyright 2002, 2012 by Chuck Hawks. All rights reserved.