cart SHOPPING CART You have 0 items

.30-378 Weatherby Magnum


Based on the giant .378 Weatherby case, the .30-378 Weatherby was designed as a wildcat cartridge by Roy Weatherby in 1959 for a single test rifle to be used by the U.S army. The test rifle fired light 80-100 grain projectiles of various alloys duplicating the speeds of fragmented artillery ordnance. The test rifle was used to study the effectiveness of both the penetrative qualities of alloys traveling at hyper velocities through armor as well as the effectiveness of armor against various alloys at hyper velocities. 
Naturally the .30-378 eventually became a sought after long range hunting wildcat cartridge. In 1996 Weatherby introduced the .30-378 as a factory loading. The .30-378 is currently chambered in three variations of the Weatherby Mk. V rifle. Typical factory loads drive 180 grain bullets at around 3400fps.
The .30-378 has retained a steady following since its introduction. The cartridge is favored by some extreme long range hunters but is also popular amongst affluent U.S hunters for shooting at ordinary hunting ranges.


The .30-378 is truly a potent magnum cartridge, slightly more powerful than the .300 RUM with an edge of around 50-100fps though variations in individual rifles muddy the waters. Its greatest strength can be found at ranges exceeding 1000 yards. Unfortunately this strength is often unrecognized and the .30-378 is instead utilized for increased wounding power at ordinary hunting ranges. The extremely flat trajectory of the .30-378 is also often utilized by hunters too lazy to take the time to learn drop compensation and although its flat trajectory is highly useful, the lazy types that often use this cartridge are just as likely to show a disinterest in shooting technique, wind drift and all other factors pertaining to optimum marksmanship for humane killing.
For those who are willing to learn, the .30-378 has a lot of reach with an effective fast killing range of around 1400 yards. I often denote 1800fps as being another cut off point below which intermediate experienced long range shooters find wind drift and other environmental factors exponentially more difficult to read. Above 1800fps, environmental factors are a lot easier to read and success rates are high amongst shooters with only moderate experience. The .30-378 is able to keep its long range bullets above 1800fps out to ranges of 980-1000 yards.
At close ranges the .30-378 places a great deal of strain on many hunting projectiles. With light conventional hunting bullets weighing between 130 and 150 grains at 3600 to 3800fps, performance can be erratic with incidents of surface bullet blow up and shallow penetration. The lighter the bullet, the stouter its design needs to be if it is to perform well at ranges inside 300 yards.
With 165 to 180 grain bullets driven at 3400 to 3500fps the .30-378 continues to place excessive strain on most projectile designs when used at close to moderate ranges - depending on body weights encountered.  Bullet designs need to be carefully matched to the job at hand. By the same token, once velocity is shed, a stout 180 grain bullet can be a slow killer on lean bodied deer again reinforcing the need for careful bullet selection.
Utilizing 200 grain bullets and heavier, the .30-378 shows more uniform performance at close to moderate ranges. On heavy animals however, there remains a great deal of strain placed on projectiles when used at close (woods) ranges. Bullet designs like the Woodleigh Magnum Weld Core and Swift A-Frame come into their own, offering immense stopping power on large bodied deer and bear at close ranges. At moderate to longer ranges, bullet designs like the 200 grain Partition produce excellent results on large bodied animals.
As ranges exceed 300 yards the .30-378 is able to make use of a wider range of projectiles including heavy frangible projectiles. The .30-378 gradually begins to show its strengths as the trajectory falls away. Through the use of dial capable scopes, trajectories can be corrected and fast, clean, humane killing delivered to medium game at long ranges.
On heavy game such as Water Buffalo the .30-378 is still limited by the .30 cal bore diameter along with excessive strain placed on hunting projectiles at typically encountered hunting ranges. The .30-378 can tackle heavy game quite adequately with careful shot placement, as can the little .308 Winchester by comparison.  But with ordinary chest shots a wider bore produces a wider wound along with deeper penetration and to this end the parent .378 Weatherby tackles what its designer intended it to tackle, with far greater authority than its .30 caliber offspring.
Due to the substantial recoil produced by the .30-378, muzzle braking is pretty much imperative. As is reiterated throughout these texts, spiral ported brakes tend to blast powder and debris into the face of the shooter. A simple side ported brake is the fix for the .30-378, the brake being removed between each shooting session to remove carbon deposits from the precious muzzle. On unbraked custom builds, all up rifle weights should exceed 12lb for accurate long range shooting. Barrel contours of #5 at 28” or longer help keep rifle weights up at 13.5lb and above.
Rifle accuracy is of paramount importance if the .30-378 is to be utilized to its greatest strengths (long range).  Make no mistake, an inaccurate .30-378 is less effective than an accurate .308 Winchester. Goal group sizes should be MOA or less, preferably in the region of .5MOA or less for shooting past 1000 yards. To achieve this level of accuracy, the shooter needs to isolate rifle errors (rifle inaccuracy) from shooter error (shooter technique). For some this may seem daunting but always remember, the deepest sense of joy and reward comes as a result of effort, not from results alone.
Long eye relief scopes are important on the .30-378 to prevent ‘Weatherby eyebrow’. This places many scope brands off the table, including some high end units such as Swarovski and Zeiss. Suitable optics should offer 4 inches of eye relief combined with controlled turret systems as opposed to simple spring loaded turrets. Most modern brake designs do minimize recoil substantially but erring on the side of caution and for all contingencies is always prudent when selecting optics for magnums.
The .30-378 is the most powerful .30 caliber on the market and to some, this translates into ‘the best’ cartridge available. But on closer examination, the .30-378 really is a specialized cartridge once its strengths and limitations are understood.
Throat life of the .30-378 Weatherby can be short with accuracy waning at around 600 rounds. Key factors in extending throat life are polishing between each shooting session; keeping the pores of the steel closed combined with attention to barrel temperatures, keeping the barrel cool which also helps prevent pores in the steel from forming. Good polishing techniques and shooting methods can extend barrel life significantly.

Factory Ammunition

Weatherby currently list seven loads for the .30-378. The lightest load features the 130 grain TTSX at a sizzling 3740fps. The Tipped TSX is well capable of withstanding these velocities and is perhaps one of the only projectiles that is able to fully utilize such a high velocity. Of the Barnes bullets, this is a good bullet weight for medium sized deer, producing fast kills out to ranges of around 400 yards (2600fps), showing sometimes delayed but clean killing down to impact velocities of 2200fps (around 540 yards). Speed of killing at extended ranges is very much dependent on target resistance with this bullet. Between the velocities of 2600 and 2400fps, fast kills can occur on well muscled game as opposed to delayed but clean killing that can occur on light game.
Mid weight loads from Weatherby include the 165 grain Ballistic SilverTip at 3500fps and the 165 grain TSX at 3450fps. The BST bullet deign is best suited to body weights between 80-120kg (180-264lb) but at 3500fps, the BST runs the risk of surface bullet blow up. From about 175 yards onwards, the BST comes into its own and continues to produce good killing performance out to ranges of around 400 yards. On Mule/Red deer sized game, this range can be extended further due to body weights offering enough resistance to initiate expansion at longer ranges (out to as far as 900 yards).
On very light or lean game however; the 165 grain BST cannot really use the ultra high muzzle velocity to any advantage as the velocity is soon lost and at moderate to extended ranges. Sure, at closer ranges and especially when major bones are hit, wounding and speed of killing can be spectacular. But killing can sometimes be quite delayed, though internal wounding is always broad. Readers need to understand that although the BST is a fragmentary projectile, relying on a cluster of fragments to produce wide wounding, the BST has a much thicker/stouter jacket than the likes of the Hornady A-Max. This has both advantages and disadvantages, the key being to understand how to work to the strengths of the projectile design.
The 165 grain TSX is a tough bullet, best suited to game weighing above 90 and 320kg (200-700lb). This bullet is about right for Elk, working best at impact velocities above 2600fps (around 325 yards) and although killing can be delayed, internal wounding remains wide down to 2200fps (410 yards).
Heavy loads from Weatherby include the 180 grain Ballistic SilverTip at 3420fps, the 180 grain Accubond also at 3420fps,the 180 grain TSX at 3360fps and the 200 grain Partition at 3160fps.  
For moderate range hunting, the 180gr BST is stuck between a rock and a hard place. Speed of killing on light bodied game can be erratic depending on whether bone is or is not encountered. Exit wounds can be either very large or regular (around .75”) in diameter.  By the same token, on heavily bodied deer the 180 grain BST can lack the penetration that many hunters expect from a .30 caliber magnum if used at close ranges. At close to moderate ranges, the 180 grain BST really comes into its own on game weighing around the 90kg (200lb) mark.
The 180 grain BST is a very good long range bullet for large bodied deer. With a BC of .507, it may not have the high BC’s of modern slippery bullet designs but does offer somewhat unique performance fragmenting at low velocities for wide wounding but doing so gradually, achieving adequate penetration on large animals. From a muzzle velocity of 3400fps, if using the BST on large heavily bodied deer of up to 320kg (700lb), the best performance parameters are between 2600fps and 1600fps or 415 to 1070 yards.  That of course, is quite some distance.  Again, even though the BC is not immensely high, wind drift and other environmental factor estimations are relatively easy to plot out to 920 yards (1800fps) with the BST, without need of the greater finesse that is required when shooting cartridges (regardless of BC) below 1800fps.
Weatherby’s 180 grain Accubond load also finds itself in somewhat of a bind.  The Accubond is a good  hunting bullet for traditional hunting ranges (300 yards) in milder magnums.  The Accubond typically sheds up to 50% weight on heavily muscled game which although is high for a core bonded bullet (The Scirocco and Interbond tend to lose about 25% weight), does help with energy transfer, usually without risk of full jacket core separation.  But in the .30-378, there is a risk of limited penetration at close ranges on large bodied game, there is also a potential risk for full fragmentation, duplicating the results of the BST. 
It is perhaps prudent to suggest that the 180 grain Accubond is best utilized on deer/sheep/antelope weighing up to a limit of 150kg (200-330lb) at closer ranges, producing fair penetration regardless of fragmentation. This puts the Accubond into the same class as traditional hunting bullets like the 180 grain Hornady Interlock. The 180 grain Accubond  gradually comes into its own as ranges exceed 150 yards, then loses its ability to initiate hydrostatic shock below 2600fps (415 yards) but continues to produce wide wounding down to velocities of 2200fps (655 yards).   In many ways, the .30-378 would be better served with the newer 200 grain Accubond.
Where great penetration is required, the 180 grain Barnes TSX is optimum. The Weatherby Barnes load does not turn the .30-378 into a Water Buffalo slayer with body shots due to the limitations of the bore diameter but the 180 grain TSX is effective on the largest of deer species.  Regardless of velocity, shot placement is the always the key to initiating fast kills with Barnes bullets.  Shots that strike too far back into the rear lungs tend to produce delayed killing (sometimes very delayed) while forwards shoulder shots produce the most dramatic results.  On angling shots, fast killing can be achieved by visualizing where the autonomous plexus lies (see game killing section), then using this as the point of aim.  Providing enough body resistance is met to initiate energy transfer, the TSX produces fast killing out to ranges of around 370 yards (2600fps).
Weatherby’s 200 grain Partition is a hard hitting bullet, creating deep and very broad wounding. Ideal for North American and Canadian large game, the 200 grain Partition shows versatility across a wide range of body weights. That said, the 200 grain load does not make the .30-378 a true heavy game cartridge due to the limitations of the bore diameter. But for large bodied medium game, this is a stellar performer, producing excellent killing out to a 760 yards (1800fps).  

Hand loading

The .30-378 Weatherby utilizes charge weights of between 100 and 120 grains of ultra slow burning powder. Reloader 25, Retumbo, H870 (spherical) and H50BMG are suitable burn rates however H50BMG is somewhat course in kernel structure and most likely has abrasive qualities when squeezed through the small .30 caliber bore.
From a 26” barrel, average velocities include 3550fps with 165-168 grain bullets, 3400fps with 180 grain bullets, 3300fps with 190 grain bullets, 3200fps with 200 grain bullets and 3100fps with 210 to 220 grain bullets. Note that no velocity is lost with the jump up to the 220 grain bullet weight, showing where the strengths of the .30-378 lay, driving long for caliber bullets at exceptionally high velocities. Rifles do tend to vary from one to the other, the velocities printed here are normally quite easily achievable while some rifles can boast velocities 100fps faster (sometimes much more) than stated.  
Readers will ask, why does the .30-378 use up to 120 grains powder to yield velocities  similar to the .300 RUM? The .300 RUM utilizes nearly twice as much freebore as the Weatherby which acts as a huge gas expansion chamber allowing for exceptionally high velocities.  The RUM case is also designed with heavy case walls at the case head to withstand higher operating pressures. At the same time, only so much energy can be transferred through a .30 caliber hole and there comes a point where increases in powder charges yield ever decreasing results. This is why Remington utilized a long freebore for gas expansion, though with the risk of decreased accuracy with individual bullet designs.  With careful load development the .30-378 can surpass the .300 RUM but once the factors of freebore, over bore (big charge / little bore),  and cartridge case pressure ratings are understood, the shooter can set realistic expectations as to just how far the .30-378 cartridge can be pushed. .
The .30-378 can be loaded with light 130 to 150 grain bullets as is found in Weatherby factory ammunition (130 grain Barnes) but problems can occur.  The twist rate of Weatherby rifles (and custom rifles) is 1:10, suitable for projectiles weighing 165 grains and heavier. In lower powered cartridges, 1:10 twist bores will adequately stabilize light bullets for general hunting but at .30-378 velocities, there is a risk of poor stability resulting in poor accuracy.  Some factory ammunition users will find that this applies to the 130 grain Barnes load in individual rifles.  Throat erosion is another problem, the higher the charge the greater the heat the greater the wear. Along with this is the problem of surface bullet blow up with conventional light weight projectiles at close to moderate ranges. The water in a small bodied deer/Pronghorn/goat can become as hard as concrete at .30-378 velocities and where the hunter might expect varminting style results, the opposite can occur. To this end, the .30-378 does its best work on medium game with bullets weighing at least 165 grains.
It is not uncommon to find 28” barreled custom rifles being used as a means to further optimize .30-378 performance as a long range hunting cartridge. Weatherby factory rifles utilize a 26” barrel while Weatherby long range models feature muzzle brakes which take the barrel length out to 29”. There are definitely gains to be had from longer barrels of up to 32”.  That said, the .30-378 really needs to be braked to aid in recoil reduction and with most brakes being around 3” long, compromises in barrel length have to be made.
Projectile choices for the .30-378 can be broken down thus, core bonded or homogenous projectiles work best when the .30-378 is utilized at close to moderate ranges, conventional hunting projectiles weighing between 165 and 180 grains begin to come into their own at ranges of around 250-300 yards while heavy weight conventional projectiles give best performance at ranges beyond 150 yards. Of course much depends on game body weights as to results. 
Frangible projectiles such as the 208 grain A-Max give best results on large animals as velocities approach 2600fps.  From a muzzle velocity of 3100fps, the 2600fps barrier is broken at 340 yards.  In rifles that can comfortably drive the 208gr A-Max at 3200fps or faster, the 2600fps barrier is broken 410 yards or beyond. At 2600fps and below, the 208 grain bullet gives an excellent balance of adequate penetration on large medium game combined with frangible wounding.
Please refer to the .300 RUM hand loading text for select projectile performance. For further exploration of projectile performance as velocities reduce over range, the .300 Winchester Magnum text serves as a base reference. One comment however, for those intending to hunt large animals with the .30-378, the 240 grain Woodleigh Protected Point is an excellent bullet.  This projectile is designed for impact velocities of 2400fps and below as opposed to the Woodleigh 200 grain Magnum Protected Point. However in practice, the very high sectional density allows for very deep penetration while the ‘softer than magnum’ bullet construction yields immensely traumatic wounding at high velocities. Jacket core separation is not an issue, neither is excessive weight loss.  The only effect that increased velocity has on this projectile at close ranges is loss of SD during penetration as the frontal area gradually rolls back on itself.  But by the time this happens, the Woodleigh has done its job, the projectile coming to rest on the offside hide of large, heavily bodied game. For tough game, this is a fast killer.

Closing  comments

Pushing boundaries is a trait of humanity, whether that be physically or intellectually. The .30-378 is most definitely a projection of this trait. And as we know, pushing boundaries can sometimes have both negative and positive consequences.
The .30-378 can be a powerful tool or a fools folly depending on cartridge utilization and shooter attitude. The strength of the .30-378 can be explained in one simple statement;  it has the ability to deliver fast clean killing on small to large bodied medium game at extended ranges. 
Suggested loads: .30-378 Weatherby magnum Barrel length: 26”
No ID   Sectional density Ballistic coefficient Observed  MV Fps ME
1 FL Weatherby 130gr TTSX .195 .350 3740 4037
2 FL Weatherby 180gr BST & Accubond .270 .507 3420 4674
3 FL Weatherby 200gr Partition .301 .481 3160 4434
4 HL 200gr Accubond .301 .588 3200 4547
5 HL 208gr A-Max (Sight height 1.8”) .313 .648 3100  
6 HL 240gr Woodleigh PP .361 .401 2900 4481
Suggested sight settings and bullet paths           
1 Yards 100 175 352 393 425 450 475 500
  Bt. path +3 +4.5 0 -3 -5.9 -8.6 -11.7 -15.1
2 Yards 100 175 330 372 400 425 450 475
  Bt. path +3 +4.3 0 -3 -5.4 -7.8 -10.7 -13.8
3 Yards 100 175 295 336 350 375 400 425
  Bt. path +3 +3.9 0 -3 -4.2 -6.7 -9.5 -12.8
4 Yards 100 175 307 349 375 400 425 450
  Bt. path +3 +4 0 -3 5.2 7.8 -10.6 -13.8
5 Yards 100 175 303 345 375 400 425 450
  Bt. path +3 +4 0 -3 -5.7 -8.4 -11.3 -14.6
6 Yards 100 150 257 296 325 350 375 400
  Bt. path +3 +3 0 -3 -6 -9 -12.5 -16.5
No At yards 10mphXwind Velocity Ft-lb’s
1 400 11.62 2587 1931
2 400 8.5 2647 2800
3 400 10 2392 2541
4 400 7.9 2557 2903
5 400 7.4 2525 2944
6 300 7.5 2241 2676
30 378 Weatherby final 
.30-378 Imperial Metric 
A .582 14.73
B .582 14.73
C R .151  
D .560 14.22
E .336 8.53
F 2.340 59.43
G .568 14.42
H 2.908 73.86
Max Case 2.908 73.86
Trim length 2.898 73.56
Discuss this article or ask a question on the forum here
Copyright © 2007-2011 Terminal Ballistics Research,


Achieve success with the long range hunting book series & matchgrade bedding products


We are a small family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing ... read more



If you find the resources on this website to be valuable, we would be sincerely grateful if you would consider making a donation to help us cover the costs of the website and to assist us to continue our research and testing into the future.  It doesn't matter whether your donation is big or small - it makes all the difference!


We are a small, family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing, and rifle accurizing.