.378 Weatherby Magnum

History

After creating the .375 Weatherby Magnum in 1944 Roy Weatherby eventually formed the opinion that his .375 was under powered. Weatherby then set about designing a .375 caliber cartridge of extreme power. In the quest for a larger case Roy Weatherby utilized the 416 Rigby as a parent case design.

For the sake of marketing a belt was added to the .416 Rigby case which, combined with the double radius shoulder, gave it a true ‘Weatherby Magnum’ appearance. The next challenge came in the form of internal ballistics. During tests it was found that the current primers of the day could not reliably ignite the massive powder charges exceeding 100 grains. To achieve consistency Federal designed the No.215 Magnum primer specifically for the Weatherby magnum. The new cartridge was named the .378 Weatherby Magnum and was introduced to the public as a Weatherby proprietary cartridge in 1953.

Up until the creation of the .375 CheyTac (post 2002), the .378 Weatherby was the world’s most powerful .375 caliber cartridge. This cartridge was also used as Weatherby’s base for the design of the .460 Weatherby.

Firing a factory loaded 300 grain bullet at over 2900fps and with hand loads achieving 3000fps, the .378 Weatherby was and remains a truly potent cartridge.

Although the Weatherby company have released their cartridges from proprietary status it is rare to find another maker of .378 brass purely because of its unique case dimensions. Due to this limited availability the .378 Weatherby is more popular in the U.S than in other countries of the world that are more dependent on common manufacture. The .378 Weatherby cannot be fireformed from existing case designs (apart from the .460 Weatherby).

 

Performance

The .378 achieves Roy Weatherby’s goals in every way. Both factory and hand loads deliver 200fps higher velocity than the .375 Weatherby, 300fps greater velocity than hand loads for the .375 H&H and 400fps higher velocity than factory .375 H&H ammunition.

When used on medium game and also large bodied deer and antelope species the .378 delivers tremendously disproportionate to caliber wounding at ordinary hunting ranges which translates into extremely fast killing.

As a large game cartridge (moose or bear), the .378 Weatherby is extremely effective. This power level is not necessary for hunting large bodied game out to ordinary ranges but is there for the taking.

When used on heavy game the increased power level of the .378 Weatherby can be considered ‘justified’. It is on heavy game that this increased power comes into its own. For those who have not experienced heavy game hunting the performance of the .378 is comparable to using a .243 or .25-06 to tackle Red or Mule deer. One cannot say that the .243 is overpowered for deer and the same applies here. Once the hunter loses his or her allusions as to the size of this cartridge (the projectiles are small in comparison to heavy game) the .378 can be seen for what it is, a well-balanced heavy game cartridge.

In my experience, by using a bullet weighing at least 250 grains driven at velocities as close to or above 3000fps this, and other cartridges of this power level, have the rare ability to initiate hydrostatic shock on heavy game causing instant poleaxe (loss of consciousness) followed by blood loss and death. The heavier the bullet and the further away we can be above an impact velocity of 2600fps the more noticeable this becomes. Obviously there are limitations to this approach. Shot placement, individual animal sizes and actual impact velocities each have to be taken into consideration. Projectile construction is another factor as this cartridge can place a great deal of stress on projectiles. For my own part, I would suggest that a very stout 250 grain bullet can produce hydrostatic shock on game weighing up to 600kg or 1300lb, but on heavier game a 270 to 300 grain homogenous bullet can prove more effective. As game weights go above 900kg (or 2000lb) the weight of the animal can overcome the ability of the bullet to produce hydrostatic shock.

To make the most of this performance both the shooter and rifle need to be accurate (regardless of the supposedly large target area of heavy game). To say otherwise only highlights the inexperience of the hunter. If hunting heavy game, get close and aim small, keeping shots well forwards as a means to maximize energy. Shoot, reload and get back on target. The stunned mullet look has no place in this game.

Unfortunately the traditional Mk V stock tends to accentuate felt recoil. Weatherby continue to utilize this design (at least at the time of writing) simply because it maintains the Weatherby look. The utter ridiculousness of this is truly amazing. The current Mk V Weatherby rifle chambered in .378 does however come fitted with a much needed muzzle brake.

For hunters contemplating building a custom .378, a straight and fat varmint style stock is the key along with a light and crisp trigger. As an example of stock design the CZ action can be mated to a Bell and Carlson Varmint stock. Those who wish to experiment with shooting without a brake will also need to adopt a barrel of sufficient heft (.825” muzzle) and aim for an all up weight of 11.5lb or more. As for the trigger, the higher the recoil, the less we want any preloading on the trigger to accentuate this. Many would disagree, I could care less what they think. Again, such arguments only highlight one’s inexperience. Those who panic and pull the trigger under threat will do so whether the trigger is 4lb or 2lb.

Factory ammunition

Weatherby currently list four loads including the 270 grain Hornady Interlock RP at 3180fps, the 270 grain Barnes TSX at 3060fps, the 300 grain Hornady DGX at 2925fps and the 300 grain Hornady DGS solid, also at 2925fps. All are generally true to or within an acceptable range of their stated velocities.

The Hornady 270 RP-SP is a relatively soft bullet of conventional construction. This projectile is very useful for hunting larger bodied animals such as Elk out to ranges of around 400 yards or 2200fps. Beyond this range shot placement and wind drift can be a concern but with great care (and practice) the Interlock can be used out to ranges of around 600 yards. But again, wind drift is a concern.

Weatherby have done well to adopt the 270 grain TSX for the .378 which produces a good balance of wounding versus penetration on heavy game. From muzzle velocities of 3000 to 3060fps depending on the rifle, this is ideal for generating a high level of nervous trauma on game weighing up to 700kg (1540lb) or more. As I have described many times now, the key is to get close (inside 100 yards) and aim small. Too often I hear of hunters speaking about the large target area of heavy game, advertising their lack of skill to all who will hear. But with an accurate rifle and careful shot placement it is possible (though not always so - depending on exact game weights) to anchor game on the spot. But, if the hunter has a flinch the .378 may wander off target by a good 3 to 5 MOA, such is the nature of these heavy magnums. The work put into practice before the hunt can pay huge dividends. Beyond its role as a heavy game load the Barnes works well on other large bodied game such as bear and moose. Having said this, best results are obtained at impact velocities over 2400fps. And again, shot placement is the key. The further one shoots the more resistance this bullet needs in order to promote expansion. For large game weighing up to 450kg (1000lb), consider 2200fps as the cut-off point.

Hornady have just now (Oct 2017) released their 300 grain round nose bonded DGX bullet. This will, over the coming weeks and months, be incorporated into the Weatherby line up, replacing the previous unbonded round nose soft point. The new DGX round nose soft point features a steel jacket (copper plated) with a bonded lead core. Unfortunately, I cannot yet report on its performance however it is my hope that this projectile will perform admirably on heavy game, backed with the DGS (solid) for follow up shots. From muzzle velocities of around 2900fps the two loads will hopefully work very well together.

A quick mention of caution must also go to the one load produced by Nosler featuring their 260 grain Accubond bullet at an advertised 3100fps. While this load is acceptable for hunting large bodied deer readers are advised to refrain from using this projectile on heavy game. Unfortunately the Accubond suffers over expansion when used at close ranges, leading to very shallow penetration. Nosler would have been better to do away with the bonding all together (Ballistic Tip) and create a load purely for extended range. But instead we have a bullet that is neither here nor there. Treat this with absolute caution.

Hand loading

As per the norm with the medium bores this cartridge does its best work on a diet of H4350 (ADI 2209).

From a 26” barrel comfortable velocities include 3350fps with 225-235 grain bullets, 3300fps with 250 grain bullets, 3250fps with 260 grain bullets, 3150 to 3200fps using 270 grain bullets, 3000 to 3050fps with 300 grain bullets and 2700 to 2800fps with the very long 350 grain Woodleigh projectiles These velocities are roughly 50 to 100fps faster than the .375 RUM with individual bore tolerances muddying the waters.

Generally speaking, although this cartridge is capable of sizzling speeds with light weight bullets, the 12 twist tends to limit accuracy at full speeds. Furthermore, very few hunters have an interest in chasing very high velocities with light pills. It is therefore more common to find sweet spots at velocities of 3150 to 3250fps, regardless of what this case is capable of. As for the heavy loads, it is most certainly worth pursuing full power provided such loads are safe and also temperature stable.

Options from Sierra include the 200 grain flat point (designed for the .375 Winchester), the 250 grain Gameking, the 300 grain Gameking and 350 grain Matchking (SMK) for long range match (primarily used in the .375 Cheytac).

The 200 grain flat point is not all that well suited to the Weatherby but it can be put to use as a mild load for hunting medium game or for general practice. Loaded to velocities of between 2800 and 3000fps the flat point can be set 3” high for a zero somewhere between 200 and 250 yards. To some the very thought of such a loading may sound absurd but when used in this manner it helps prevent dust collecting on one’s rifle while proving immensely effective on medium game.

The 250 grain Gameking features a jacket nearly twice as thick as other Gameking bullets along with an extra tough core. This is an outstanding bullet when used in the .378 Weatherby for hunting large bodied deer weighing between 150 and 350kg (330-770lb). The 250 grain Gameking can normally handle heavier body weights but when loaded well over 3000fps there is a risk of shallow penetration. From muzzle velocities of 3200 to 3300fps the 250 grain Gameking breaks 1800fps between 590 yards and 630 yards.

The 300 grain Gameking was designed to cope with .378 velocities. Nevertheless, there are some limitations. This bullet is very useful for open country work on large thin skinned game weighing up to 600kg (1300lb). But when used on potentially dangerous animals it can be best to consider 450kg (1000lb) as a maximum body weight. If the Gameking is forced to penetrate through more than a foot of tissue and bone combined with high impact velocities it sheds a great deal of energy. It can therefore be wise to dual load, utilizing a premium bullet for close range work where raking shots may have to be taken on dangerous animals, utilizing the Sierra for open country work. Those who hunt in mountainous terrain where ridge to ridge shots are to be expected will greatly appreciate the heavy Sierra bullet. From a muzzle velocity of 3000fps the 300 Gameking breaks 1800fps at around 675 yards.

Sierra’s 350gr SMK is designed for target shooting only. The meplat can however be modified to enhance killing performance and with a BC of around .8 this bullet can afford to lose a whole point in BC without ill effect. Those who put BC ahead of killing take note: hitting and killing are two different things. Following modifications and provided the mods are truly successful and that game animals are of a large size as to offer suitable resistance this bullet has some merit for extended range hunting. Having said this, long range shooters are advised to look to the Rocky Mountain ULD bullet for dedicated long range killing. Readers are also asked to avoid any magical high weight retention bullets that supposedly dump maximum energy yet retain 100% weight, defying physics without a shred of common sense. More information on this subject can be found in The Practical Guide To Long Range Hunting Cartridges.

Hornady projectiles include the 250 grain GMX, the 270 grain Interlock RP-SP, the 300 grain DGX and the 300 grain DGS.

For the sake of posterity, the now obsolete 225 grain Hornady Spire point Interlock was an excellent choice. Kills inside 200 yards were spectacular, though meat damage was severe at close ranges. Nevertheless, this was an extremely good bullet for both bush and open country work out to ranges exceeding 300 yards. I long for the day when either Hornady or Sierra revisit this bullet weight.

The 250 grain GMX (homogenous copper) projectile is an excellent bullet for hunting large bodied game out to moderate ranges. This projectile is at its best at impact velocities over 2600fps. In the .378 Weatherby, high muzzle velocities of 3200 to 3300fps help a great deal to generate hydraulic wounding on game weighing up to 600kg (1300lb). There is a small risk of petal loss when the GMX is used in this manner though this makes little difference to its performance. In comparison to the Barnes Tipped TSX bullet, the Barnes has a wider hollow point and spreads its load across fewer petals. The GMX has extra notches within its ogive resulting in smaller petals which can allow the ogive to swage back in a more uniform manner. But when all is said and done both perform in much the same manner relative to the strengths and limitations of homogenous copper projectile design.

Due to the fact that Hornady have only just released the bonded DGX, I cannot yet comment on its performance. Hopefully this will prove to be a very reliable projectile and especially well suited to the .378 Weatherby. The previous Hornady iterations of the dangerous game bullet were not all that well suited to impact velocities above 2900fps. The brass Interbond bullet was the worst, suffering bullet blow up on impact. It is certainly interesting to see how this projectile has progressed over time and good to see Hornady have been willing to make improvements as needed.

Speer bullets include the 235 grain semi spitzer Hotcor, the 270 grain BTSP and the 285 grain Grand Slam.

The 235 grain Speer Hotcor can be put to good use in the 378. In lesser cartridges this bullet can at times be somewhat annoying. Like the Accubond, its core bonding can be too weak for use on large game but too stout for light game, yet by the nature of its bullet weight should in theory be suited to lighter medium game. Instead it often does its best work on large bodied deer and antelope and although there is ample scope for this, it is still somewhat of a shame that Speer do not produce a true light to medium weight game bullet for .375-08 and .375-06 users. But in the bullet melting Weatherby the 235 grain Speer can be viewed as truly soft. From an easy muzzle velocity of 3200fps the Hotcor is an emphatic killer of medium game down to an impact velocity of 2400fps or around 250 to 260 yards. Between 2400 and 2200fps (330 yards) wounds are wide but we may see a slight delay in killing. Below 2200fps and through to the cut off point of 1800fps we see a more noticeable delay while shot placement is also made more difficult as a result of wind drift (BC .301). In any case, this is a very spectacular killer of lean to medium sized game when used in the .378 Weatherby.

The 270 grain Speer BTSP loaded to 3150fps is an exceptional killer of large bodied game. This can be used in the same manner as the Sierra 250 grain bullet. On light framed game this bullet does its best work down to impact velocities of 2600fps or around 250 yards. Between 2600 and 2200fps (450 yards) the Speer produces clean but sometimes delayed kills on light framed game animals depending on shot placement. Below 2200fps and through to 1800fps (680 yards) shots must be kept well forwards in order to ensure clean killing. But with a BC of only .429 this can be difficult in higher winds. As a long range bullet for large bodied deer and antelope the Speer is simply outstanding down to 1800fps. Those who wish to push this further need to understand that the Speer can really struggle to produce any form of expansion between 1800fps and 1600fps (800 yards). Body weight resistance must be high and shot placement must be sound.

The Speer Grand Slam is a premium bullet but after having had several bad experiences with this bullet I cannot recommend its use, especially at .378 Weatherby velocities.

Nosler projectiles include the 260 grain Accubond, the 260 grain Partition, the 260 grain Banded Solid, the 300 grain Accubond, the 300 grain Partition and 300 grain Banded Solid.

Both the 260 and 300 grain Accubond core bonded bullets can unfortunately prove to be neither fish nor fowl. The bonding is too weak for heavy game work yet too soft for extended range work. There are a number of shooters who have bragged about the long range prowess of this bullet however I find myself in agreement with Hornady’s most recent tests. These are most suitable for large bodied deer or antelope out to ranges of around 400 yards. Used in this manner the Accubond can be highly effective. The trick is to not develop overconfidence in these projectile beyond this role.

The two Partition bullets can each be put to good use in the .378 Weatherby. Having said this, the .378 does place a great deal of strain on the Partitions. Both work well on large bodied deer or antelope weighing up to 600kg (1300lb). Neither should be used on dangerous animals weighing over 450kg (1000lb) at close ranges. Those who wish to hunt Brown bear weighing less than 450kg may find that the 300 grain Partition offers an excellent balance of wounding versus penetration. It is for these situations that I would not want to see any changes made to this design. The only change that could possibly be made is some form of rear core bonding, avoiding any changes to the front core. The Partition also has fairly good reach, being immensely effective on appropriate game out to ranges of around 360 yards or 2200fps. Between 2200 and 1800fps (570 yards) shot placement must be sound which can be hard to guarantee with a BC of .4 in high winds.

Barnes bullets include the 235 grain TSX, the 250 grain Tipped TSX, the 270 grain TSX, the 300 grain TSX and the 350 grain TSX. Barnes also produce flat point lead core bullets designed for the .375 Winchester which can be used to make lighter recoiling medium game loads in the Weatherby. I generally use the slower burning 4831 burn rate powder when developing mild loads (also when loading the Sierra flat point) but have also used full charges of H1000.

The 235 TSX has a relatively low BC of .270. Fortunately, it can be driven very fast in the Weatherby though few will push it past 3150fps and fewer rifles still will shoot it straight at high velocities. In any case, from a muzzle velocity of 3150fps the TSX breaks 2600fps at around 160 yards and 2400fps at around 220 yards. Beyond 220 yards this bullet is best suited to large bodied non-dangerous game which offer plenty of body weight resistance to aid expansion and hydraulic wounding. Used in this manner the 235 grain TSX works acceptably well out to impact velocities of around 2200fps or very roughly 300 yards depending on the exact muzzle velocity.

The heavy Barnes bullets are designed for large, tough game. Of the available designs the 270 and 300 grain bullets have great merit for use on game weighing over 450kg and up to 900kg (2000lb) while the 350 grain bullet is best reserved for the heaviest of game. In each and every case, my advice when using these projectiles is to load as fast as the rifle will accurately allow, get close and break bone. The TSX performs admirably when used in this manner and really brings the .378 into its own.

Swift projectiles include the 250, 270 and 300 grain A-Frame’s along with their new Break away solids (untested at the time of writing).

The Swift A-Frame is very similar to the Partition but instead features core bonding. For my own part, I am glad the two brands are not identical as each offer unique performance. The A-Frame, while very tough, is more limited in its effective range. The Partition can excel when used to shoot across valleys. The A-Frame, in contrast, comes into its own at closer ranges. Furthermore, by deliberately stalking in close we can put the increased power of the .378 to use in a meaningful and measurable manner. While both the 250 and 270 grain bullets work very well on larger bodied game, it is the 300 grain bullet that will be of most use to the .378 user. Driven hard the A-Frame sheds some weight and SD, but manages to smash though heavy bone and achieve very wide internal wounding. This bullet is most useful on game weighing up to and around 600kg (1300lb) while 700kg should be considered the upper limit. On heavier game a homogenous bullet can prove more effective.

Woodleigh produce both round nose and protected point Weldcore projectile designs. Owners of .378 (and RUM) rifles are advised to select stouter protected point available in 235, 270, 300 and 350 grain weights. Having said this, those who wish to use Woodleigh bullets on game weighing no more than 450kg (1000lb) will find that the 300 grain round nose produces immense trauma and is the more versatile where game weights vary by a good deal. This bullet is not designed to be used at impact velocities over 2400fps, but provided it is not used on heavy game, produces exceptional results

Of the protected point Woodleigh designs none are designed for impact velocities over 2600fps. Nevertheless, they can work very well. The 300 grain bullet (one of my go-to bullets) is effective on game weighing up to 600kg (1300lb). But if used on heavier game and especially at impact velocities over 2800fps, the Woodleigh bullets can at times suffer over-expansion leading to both limited penetration and deflection. Therefore, while it can be enjoyable to push the limits, hunters must apply caution. 

The 350 grain Woodleigh is designed to be used at impact velocities no higher than 2500fps. But again, I like to push the envelope a bit. The high sectional density of the 350 grain bullet helps immensely with straight line penetration, adding some reliability when hunting game in the 600 to 700kg (1300 - 1540lb) weight range. But alas, on dangerous game the Woodleigh does not have the same level of reliability that can be derived from a homogenous bullet design.
 

Point A shows the bullet impact on this feral cattle beast which dropped the animal on the spot. The animal was almost fully broadside (just quartering on), the bullet broke the humerus (leg raised to show break). Under ideal conditions, I would normally wait for a true quartering on shot and aim at point B, the joint intersecting the humerus and scapula.
 

Closing comments

The .378 Weatherby is an exceptionally good cartridge for hunting large game. But to utilize it the hunter must get past the initial grandeur of high power and see it for what it really is. Clear of any illusions, the hunter can get down to business and focus on load selection and rifle accuracy while all the time working towards the goal of minimal human error.

This is a wonderful cartridge for those willing to take the time to get to know it.

Sight height 1.6” (Scope).

*Load 1, 2 and 6 set for heavy game / close range.

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