The .375 Caliber Cartridge Family
(.375 H&H Mag., .375 Wby. Mag., .375 Win., .376 Steyr, .375 Dakota, .378 Wby. Mag., .375 Ruger, .375 Flanged Magnum)

By Chuck Hawks

Not all rifle calibers are named for their actual bullet diameter, but the .375 family of cartridges actually use .375" diameter bullets. Holland & Holland of London put .375 caliber cartridges on the map when they introduced their .375 Belted Rimless Magnum and companion .375 Flanged Magnum in 1912. The belted rimless version was intended for repeating rifles, while the flanged (British for "rimmed") version was for single shot and double-barreled rifles.

In the USA and most of the world today the .375 H&H Belted Rimless Magnum is known simply as the .375 H&H Magnum and it is probably the most popular dangerous game cartridge in the world, used from Alaska to sub-Saharan Africa to harvest outsized animals. The common bullets weights are 235, 270 and 300 grains.

Assuming proper bullet construction, the 235 grain bullets (SD .239) at around 2800 fps are primarily intended for those who wish to use their .375 rifles on Class 2 game. The 270 grain bullets (SD .274) at around 2650-2700 fps are generally adequate for all Class 3 game, as well as the largest and most dangerous predators, especially lion and the great bears. The money load is a 300 grain (SD .305) soft point or solid (FMJ) bullet at a muzzle velocity (MV) of about 2500 fps with 4160 ft. lbs. of muzzle energy (ME) from a 24" barrel. 300 grain bullets are generally intended for use on thick skinned, dangerous animals.

The flanged version, loaded to somewhat lower pressure, launches a 235 grain bullet at about 2750 fps, a 270 grain bullet at 2600 fps, or a 300 grain bullet at about 2400 fps with ME of 3835 ft. lbs. The difference in terminal effect is minimal and either of Holland's .375s will drop anything from elephant on down. In some African countries the .375 H&H is the minimum cartridge legal for hunting lion, buffalo, rhino, hippo and elephant.

Because bolt action rifles are much less expensive than double rifles, not to mention that they generally hold three or more cartridges and are more accurate, the .375 H&H Belted Magnum is much more common than the flanged version. Its popularity is limited mostly by the fact that it is a long, full length magnum cartridge that requires a rifle with a long magnum action, which not all manufacturers offer.

Long Mauser 98 actions were supplied for the .375 H&H Magnum from the beginning, but it was not until the Winchester Model 70 was introduced in 1936 that a mass produced American bolt action rifle was designed to accommodate the .375 H&H. Today Winchester, Browning, CZ, Remington, Ruger, Weatherby, Nosler and others offer rifles in .375 H&H Magnum.

The fame and popularity of the .375 H&H Magnum has spurred the introduction of a number of other .375 caliber cartridges. Some of these are more powerful than the original, some are intended to approximately duplicate the performance of the original in standard (.30-06) length bolt actions and some are less powerful, but kick less than the original.

In the more powerful category, the best known examples are probably the .375 Weatherby Magnum, .375 Remington Ultra Mag and .378 Weatherby Magnum. All of these launch 300 grain bullets faster than the original, thus achieving a flatter trajectory and increased energy downrange.

Since the .375 H&H Magnum is not lacking for killing power at the moderate ranges at which dangerous game is usually shot, these more powerful .375s are not necessarily more deadly, but they deliver .375 Magnum killing power at longer distances. The drawback, of course, is significantly increased recoil and muzzle blast.

The .375 Weatherby Magnum is an "improved" cartridge, based on a blown-out .375 H&H case. The result is enough extra powder capacity to increase the MV of a 300 grain bullet to 2800 fps from a 26" barrel when the cartridge is loaded to the higher maximum average pressure (MAP) typical of Weatherby cartridges. Because it is an improved version of the .375 H&H parent cartridge, not an entirely new cartridge, .375 Weatherby rifles can also shoot regular .375 H&H Magnum cartridges. The .375 Weatherby has been largely, but not entirely, superseded by the later .378 Weatherby.

The .375 Remington Ultra Mag (RUM) is based on a blown-out .404 Jeffery case slightly shortened to the same 2.850" case length as the .375 H&H Magnum. The maximum cartridge overall length (COL) is also the same as the .375 H&H, at 3.60". This non-belted, rebated rim case is fatter than the .375 H&H case and therefore can hold more powder. The result is a 300 grain bullet at a claimed MV of 2760 fps from a 24" barrel. The future of the .375 RUM is currently in doubt, as Remington has not chambered rifles for the cartridge in several years.

The .378 Weatherby Magnum, despite its odd nomenclature, uses standard .375" bullets. It is based on a necked-down, blown-out, belted version of the giant .416 Rigby elephant rifle case. Jack O'Connor, the Dean of American gun writers, showed Roy Weatherby a .416 Rigby cartridge and the rest is history. (O'Connor had been developing reloads using US canister powders for his Brevex Mauser action based .416 Rigby rifle.)

The .378 Wby. case can hold a maximum load of 112.0 grains of IMR 7828 powder, enough for reloaders to drive a 300 grain bullet at a MV of 2900 fps. The Weatherby factory load drives a 300 grain bullet at 2925 fps and 5699 ft. lbs. Not surprisingly, the .378 Wby. Mag. is known as one of the world's hardest kicking cartridges.

Among cartridges intended to essentially duplicate the performance of the .375 H&H Magnum the best known are probably the .375 Dakota and .375 Ruger. The .375 Dakota is a successful proprietary cartridge based on a shortened and necked-down .404 Jeffery case. The rim and case head diameter is .545" and the maximum COL is 3.330". The intention was to essentially duplicate the performance of the .375 H&H in a standard length, but fatter, case.

Although it is a .30-06 length cartridge, the .375 Dakota requires a fatter bolt head and wider magazine than standard length belted magnum cartridges, such as the 7mm Remington Magnum and .300 Winchester Magnum, which has limited its popularity. As far as I know, only Dakota rifles are regularly chambered for the cartridge. The advertised MV with a 300 grain bullet is 2600 fps.

The .375 Ruger, designed by Hornady and Ruger to fit in standard length Ruger M77 rifle actions with standard width magazines, is based on a new, non-belted, rimless case with a standard magnum .532" rim diameter and a .532" head diameter. Very little case taper, a sharp 30 degree shoulder angle and a very short neck maximize powder capacity. Its advantage over the .375 Dakota and other .375s based on fat cases is that it can be used in any commercial action that accommodates .30-06 length belted magnum cartridges, such as the 7mm Rem. Mag., .300 Win. Mag, .338 Win. Mag., etc.

The .375 Ruger was designed with the latest generation of powders in mind. One of Ruger's goals was to achieve .375 H&H performance in a shorter rifle. While the Ruger M77 Hawkeye African model comes with a 23" barrel and is 44.88" in overall length, the Ruger Guide Gun features a 20" tube and an overall length of about 42". Incidentally, these Ruger rifles have a catalog weight of eight pounds, which is far too light to moderate the kick of such a powerful cartridge, so the recoil is fierce.

Commercial .375s that were not designed to at least equal the performance of the .375 H&H Magnum have not fared well in the marketplace. The two most notable examples are the .376 Steyr and the .375 Winchester.

The .376 Steyr, which uses standard .375" bullets, was designed by Hornady for Steyr Mannlicher. Introduced in 1999 in the Steyr Scout rifle, the .376 is based on slightly shortened and necked-up 9.3x64mm Brenneke case. It is designed to work in standard length actions. The rim diameter is .495", head diameter is .506" and the maximum COL is 3.110". Steyr no longer offers rifles in .376, so the cartridge is apparently headed for obsolescence.

Factory loaded ammunition is offered by Hornady with 225 and 270 grain bullets, the latter at a MV of 2600 fps from a 24" barrel. Hornady does not offer a factory load with a 300 grain bullet, although reloaders can drive such bullets at 2400-2500 fps from a 25.5" barrel with maximum loads. The .376 Steyr thus closely approximates the performance of the .375 H&H Flanged Magnum.

Unlike the other modern .375 cartridges addressed in this article, the .375 Winchester is a rimmed cartridge designed for the Winchester Model 94 lever action rifle. Introduced in 1978 in the Winchester Big Bore 94, it was adapted to the Marlin 336 lever action in 1980. Savage also turned out a few Model 99s in the caliber. As far as I know, these are the only production lever rifles offered in .375 Winchester and the .375 caliber versions are long discontinued, although Winchester still offers .375 factory loaded ammo.

The .375 Winchester is based on a strengthened .38-55 case, which was also the parent case for the .30-30. The rim diameter is .506", the head diameter is .420", the case length is 2.020" and the maximum COL is 2.560". The .375 is loaded to considerably higher pressure than the .38-55 (52,000 CUP, compared to less than 30,000 CUP). Never attempt to shoot .375 Winchester ammo in a .38-55 rifle.

The .375 Win. was initially offered with a 200 grain Power Point bullet at 2200 fps intended for hunting Class 2 game and a 250 grain Power Point bullet at 1900 fps adequate for Class 3 game. The sole surviving Winchester factory load is the 200 grain bullet (SD .203) at a MV of 2200 fps and ME of 2150 ft. lbs. This is a moderate range brush/woods load. Its ballistics are superior to the .35 Remington, but inferior to the .358 Winchester.

Reloaders can increase the terminal performance of the .375 Winchester by using maximum powder charges behind the 220 grain Hornady InterLock Flat Point bullet (SD .223), which is designed for Class 2 and Class 3 game. MVs of 2200-2300 fps can be attained from a 20" barrel. Although not a commercial success, the .375 Winchester remains a fine woods cartridge.

Hunters with modern .38-55 Winchester rifles, such as the post-1964 commemorative Winchester Model 94s and the current Miroku produced rifles, can exceed the killing power of the .375 Winchester with heavy .38-55 +P loads, such as the Buffalo Bore Heavy .38-55 load. This is a 38,000 CUP load, the same MAP as the .30-30, that launches a .377" diameter, 255 grain bullet (SD .256) at a MV of 1950 fps and ME of 2153 ft. lbs.

The bonded core construction and higher sectional density of this jacketed flat nose (JFN) bullet makes it a better choice for hunting large animals. This load has been proven on the largest Alaskan game, including moose and grizzly bear. Incidentally, Buffalo Bore states these cartridges can safely be fired in ALL .375 Winchester rifles.

In closing I should mention that modern .38-55 Winchester Model 94s have a .377" groove diameter and the correct bullet diameter is therefore .377". .375" bullets will normally expand enough to engage the rifling in .377" barrels upon firing and the Buffalo Bore JFN bonded core .377" bullet will safely size down when fired in .375 Winchester barrels.

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Copyright 2016 by Chuck Hawks. All rights reserved.