7mm Weatherby Magnum

History

The original introduction date of the 7mm Weatherby is unclear, however its appearance in the early 50’s came at a similar time to the 7x61 while predating the 7mm Remington magnum by almost a decade. Roy Weatherby further monopolized his market by retaining patent rights to his designs, being the only manufacturer legally allowed to supply ammunition for his cartridges. Had other manufacturers supplied Weatherby ammunition during the formative years, it is likely that the Weatherby designs would have become the most popular magnums of the 20^th century. Nevertheless, the exclusive nature of the 7mm Weatherby limited its popularity.

Although the 7mm Weatherby was readily available throughout the U.S, wildcatters continued to experiment with home grown designs based on the same .375 (and .300) Holland & Holland parent case design. The Weatherby rifle design was also quite often regarded as garish, compounding a general lack of mainstream popularity. One promising wildcat, dubbed the 7mm Mashburn Super magnum, was brought to the attentions of Remington ballisticians. This design along with the limited success of the 7mm Weatherby combined with a market demand for magnum powered cartridges prompted Remington to develop the 7mm Remington Magnum, a cartridge which proved so popular that it flattened many other competing cartridge designs almost overnight.

For several decades, the 7mm Weatherby dwindled in popularity until eventually, new marketing techniques from Weatherby re-injected life into it. The Weatherby mark V rifle saw extensive aesthetic remodeling during the mid to late 1990’s resulting in both cleaner, simpler styling at more affordable prices.  Weatherby also eventually leased rights to produce ammunition to Federal. Along with these major factors, the general desire of the hunting market to explore new options, new (and classic) cartridges, lead to a steady revival of the 7mm Weatherby Magnum.

Today, the Weatherby is enjoyed by a wide range of hunters around the world. This cartridge is also favored by a small number of long range hunters.
 

Performance

The 7mm Weatherby has almost identical case capacity to the 7mm Remington Magnum. The major difference between the two, is the design of the rifle chambers. The Weatherby rifle chamber features a long free bore while the Remington is quite the opposite, in some instances almost strangling its loads.  Free bore refers to the area of the rifle chamber, beyond the case neck but before the start of the rifling. In this area, the bullet does not touch the chamber walls as it leaves the cartridge case, prior to engaging the rifling. Long free bore can be used as a pressure release area, allowing a gradual build up of pressure over time. In WW1 and WW2 era military bolt action rifles, free bore was common as a result of chambers being cut to suit original round nose bullet designs, but later loaded with pointed bullets with shorter bearing surfaces. The 6.5x55, 7x57 and 8x57 are common examples.
 
The long free bore of the 7mm Weatherby allows for greater potential velocities than is achievable in standard 7mm Remington Magnum chambers. That said, to some extent, excessive free bore can occasionally be detrimental to accuracy. If a short projectile is used, a moment occurs during firing, where the projectile is neither guided by the case neck nor engaged in the rifling. In this situation, the short, unguided projectile, can have a tendency to enter the rifling at slightly non concentric angles. Generally speaking, the faster the twist rate, the greater the yaw, the lighter the bullet (greater distance to travel from case neck to rifling), the greater the yaw and finally, the higher the velocity, the greater the yaw. This type of yaw can be referred to as ‘bullet stability’. Ultimately, the Weatherby, like most cartridges, has its strengths, its weaknesses and its limitations.
 
In terms of power, the 7mm Weatherby produces a level of power that is exceptionally well suited to the vast majority of the worlds medium game species at both close and long ranges. Clean killing, spectacular wounding, broad wounding, adequate penetration with suitable bullets are all terms that fit the 7mm Weatherby comfortably. Furthermore, recoil in suitably fitted rifles can be considered moderate - providing good shooting habits are understood and maintained.
 
The 7mm’s, including the magnums, tend to reach their limit on game weighing over 320kg (700lb). On large heavy game with ordinary front shoulder shot placement, the 7mm magnums can produce adequate penetration however wider, heavier bullets produce wider wounding and faster bleeding, resulting in faster kills.

   

Factory Ammunition

Current loads from Weatherby include the 120 grain Barnes TSX at 3430fps, 139 grain Hornady Interlock at 3340fps, the 140 grain Partition at 3303fps, the 140 grain Barnes TSX at 3250fps, the 150 grain Nosler Ballistic Tip at 3300fps, the 150 grain Barnes TSX at 3100fps, the 154 grain Hornady Interlock at 3260fps, the 160 grain Nosler Partition at 3200fps, the 160 grain Nosler Accubond at 3060fps and finally, the 175 grain Hornady Interlock at 3070fps. Weatherby sporting rifles always feature 26” barrels and due to the fact that Weatherby use a 26” test barrel, velocities with Weatherby factory ammunition usually duplicate factory specs. 

The Weatherby/Hornady loadings are best suited to light bodied medium game, these loads are Weatherby’s budget offerings. The 139 grain Interlock is fairly lack luster in comparison to the 154 grain bullet which is in some ways, more emphatic in both wounding and penetration on game weighing up to 80kg (180lb). Neither of these projectiles have exceedingly high BC’s compared to, for example, the 154 grain SST and InterBond which would be a better dual offering although counter to budget requirements. 

The 175 grain Interlock is another oddity. This projectile is too soft, especially at magnum velocities, to be useful on heavily bodied game due to a tendency to suffer bullet blow up at close ranges. While the 175 grain Interlock is usually capable of superb accuracy, it is a pity that this bullet does not feature a boat tail to lift its BC from a mild .462 to a more generous .550. Nevertheless, when used as a medium game bullet, the 175 grain Interlock produces spectacular wounding at close ranges coupled with adequate penetration.  Based on the current designs and costing, Weatherby would be far better to adopt the 162 grain Interlock BTSP (BC.514) and do away with the rest.

The 140 grain Partition load is ideal for lighter medium game however, as is reiterated throughout the 7mm texts, the 140 grain bullet weight with its low SD and typically low BC’s is not the most spectacular nor emphatic killing bullet weight in the sevens, regardless of magnum muzzle velocities. Still, the 140 grain Partition is a good bullet for light or lean bodied deer, goat and sheep. The 150 grain Ballistic Tip is also good for the same range of game and with a BC of .493, is a useful intermediate long range bullet which by its own unique virtues, produces wide yet relatively deep wounding (broadside) out to around 575 yards.

Weatherby’s 160 grain Partition and Accubond are two of the very best bullets available for use in the 7mm magnums. Both of these projectiles are very fast expanding, producing wide wounding on all body weights up to around 320kg (700lb) which is somewhat near their limit. Of the two, that grand old design, the 160 grain Partition at 3200fps, is the more violent wounding and is particularly useful in anchoring animals under difficult circumstances such as woods/bush hunting, not only at point blank ranges but also ridge to ridge, out to 525 yards (2200fps). The Weatherby Accubond load is slow in comparison to typical top loadings for this cartridge. Perhaps Weatherby were unable to obtain full velocities with their preferred powder choice. Whatever the reason, the Accubond load is not nearly as dramatic as its Partition counterpart. These comments aside, one benefit of mild velocity is that on larger animals such as Elk, the Accubond is not pushed to the point of suffering excessive weight loss during penetration. Both the Partition and Accubond are prone to problems in extreme conditions such as, when striking the ball joints of game weighing around 400kg (880lb). As loaded by Weatherby, the 160 grain Accubond at 3050fps produces wide wounding inside 275 yards (2600fps), gradually tapering off as velocity approaches 2400fps or 375 yards. 

The 120 grain Barnes TSX is a relatively new offering from Weatherby. Generally speaking, the 120 grain TSX is a more violent, broader wounding lighter medium game bullet than the heavier 7mm TSX bullets. This is simply because of the combination of high velocity versus low SD, causing greater resistance at the target however there is one factor that limits the performance of this projectile - its low BC of .349. All of  the TSX bullets produce high shock down to 2600fps and broad wounding down to 2400fps. The 120 grain TSX breaks the 2600fps barrier at 300 yards and 2400fps at around 375 yards which is much more limiting in ‘useful’ range than the 140 grain TSX offering.

Weatherby’s 140 grain TSX load is excellent for game weighing 80kg and heavier out to ranges of around 325 yards (2600fps) and 425 yards (2400fps) at a push. The 140 grain TSX is one of the better Elk bullets in the 7mm range, regardless of its seemingly low weight. On game weighing less than 80kg, the 140 grain bullet is effective at producing fast kills above 2600fps and clean but slightly delayed kills down to 2400fps however its performance is somewhat under utilized (perhaps unnoticeable is a better word) when used on light bodied animals. For best results at extended ranges, the Barnes TSX bullets should always be angled into major bones to initiate maximum trauma to both vitals and the central nervous system. By the same token, at longer ranges where careful shot placement is needed, environments that produce gusting winds above 10mph can make exact shot placement virtually impossible.

Federal produce two loads for the 7mm Weatherby, the 160 grain Trophy Bonded Bear claw at 2990fps and the 160 grain Accubond at 3100fps which duplicates the Weatherby factory load. The TBBC is a very tough projectile, similar in performance to the Barnes TSX and does its best work on heavy animals and when driven through major bones.
 

Hand Loading

 
Brass for the 7mm Weatherby Magnum is readily available throughout the world however, in a pinch, 7mm Remington Magnum brass can be re-formed to Weatherby dimensions thanks to the belt which helps create a positive reference point during fire forming.
 
The most suitable powders for reloading the 7mm WBY are the slow to ultra slow powders. Those in the 4831,N165 range are adequate for 139/140 grain bullets but not ideal for heavier bullets. Slower H1000 and Retumbo (ADI2225) deliver maximum velocities with bullet weights of 150 grains and heavier. Achievable velocities from  26” barrels include 3400fps with 140 grain bullets, 3300fps with 150 grain bullets, 3200fps with 160 grain longsters and 3000fps with 175-180 grain bullets. That said, individual rifles and bullets may show more desirable accuracy and optimum case life 50fps below the above listed averages.
 
As already mentioned, the 7mm Weatherby has long free bore. Weatherby factory ammunition (Partition) features a COAL of 3.360” (85.3mm) for a bullet jump of .378” (9.6mm), or there about, depending on individual chamber dimensions. Hand loaders can seat projectiles out further in order to decrease bullet jump however bullet jump still remains somewhat long, usually around a quarter inch. If a pointed bullet is seated closer to the lands, bullet to bore alignment suffers with shallow seating depths.
 
As far as free bore versus accuracy potential goes, a good comparison can be found in the .308 Winchester. This cartridge has a bullet jump of .157” (4mm), which is dictated by the magazine length of short action rifles. Heavy barreled .308’s are easily capable of shooting inside .25 MOA with this bullet jump. The longer free bore of the Weatherby can pose potential accuracy problems with some bullet/powder combinations. Experimentation with differing brands of bullets is vital if extreme accuracy is the ultimate goal. 
 
Weatherby use a rifling twist of 1:10” which may not sound ideal for 160 to 180 grain bullets however this twist rate has its benefits. Long free bore can allow projectiles to enter the rifling slightly off center. This occurs because during firing, there is a moment when the projectile is neither engaged or guided by the case neck nor engaged in the rifling, traveling through the free bore portion of the barrel which is slightly over sized. If the twist rate is too fast, any minor misalignment is magnified, creating excessive bullet yaw and ultimately poor accuracy.
 
In a fast twist rate of 1:9” with, for example, the 162 grain SST and especially the 168 grain VLD, increases in velocity above 3050fps will sometimes  produce ever widening groups until, at 3200fps, group size is out to around 3 MOA. In contrast, the hand loader using a 1:10 twist barrel in the 7mm Weatherby can to some extent avoid the problem of excessive yaw and in some instances, the faster the load is driven, the greater the accuracy potential.
 
As for ideal seating depths, projectiles are best seated into the case neck to depth of at least .284” (7mm) for optimum bullet to bore concentricity. This and the usable magazine length are the two factors to be aware of when hand loading for long free bore chambers.
 
Generally speaking, in the 7mm Weatherby, a good rule of thumb for bullet construction selection for medium game is to choose either a light and stout (139-140 grain) bullet or a heavy, soft bullet.
 
Due to a combination of reasons, many 140 grain 7mm projectiles produce fairly lack luster performance on medium game, whether driven from the 7mm08, the 7mm Weatherby or 7mm RUM. Of the available 139/140 grain projectiles, the most notable performers (at magnum velocities) include the 139 grain Hornady InterBond and the 140 grain Nosler Accubond. These are not ideal long range projectiles for this long range capable cartridge but are very emphatic out to ranges of around 400 yards on lighter bodied medium game.
 
The 139 grain SST, which performs so well at 7mm Remington Magnum velocities of 3200-3250fps (24” barrel) is pushed beyond its limits when driven at 3400fps and used on light through to medium weight game at close ranges inside 100 yards. This is the one area that the ultra velocity sevens suffer, at impact velocities above 3200fps, 140 to softer 162 grain projectiles can sometimes meet so much resistance at the target, that the projectile is unable to deliver hydrostatic shock. Wounds may be large however, because the central nervous system often fails to register what has just happened, the game animal escapes, covering a vast amount of ground before succumbing to blood loss.
 
The 154 grain Hornady SST is a generally excellent bullet although at Weatherby velocities, can struggle to stay together with close range shots, especially on large bodied game. The 154 grain SST has a fairly good BC of .525, perhaps less than ideal in comparison to recent bullet designs but nonetheless effective at long range. In the field, broadside shots on medium game tend to be extremely dramatic out to 475 yards with a slight reduction in wounding potential at the 2000fps barrier. Out at 900-1000 yards, where wounding is purely a result of bullet mechanics in the absence of high velocity, the SST continues to produce wide wounding if bone is hit, a most surprising yet uniform result. The 154 grain SST does suffer more wind drift than the likes of the VLD bullet design however in the hands of an experienced shooter, this projectile can be used to extremely great effect. The 154 grain SST has a 154 grain InterBond counterpart that shoots to the same POI and once the InterBond is annealed (see 7mm Rem Mag) produces violent wounds inside 300 yards and produces deep penetration on all medium weight game. The 154 grain SST derives little benefit from annealing.
 
One of the very best magnum seven projectiles is without a doubt, the 162 grain Hornady SST. This is an excellent all round, medium game bullet blessed with the ability to produce wide, deep, free bleeding wounds. This and the 180 grain Berger VLD are two of the most useful bullets in the 7mm magnums. 
 
For best results at all ranges, the 162 grain SST should be annealed. This softens the ogive of the SST allowing it to swage back and reduce frontal area during penetration, resulting in much deeper wounding.  A second major benefit is that at long ranges where velocity is low, the SST expands more readily. As far as total penetration is concerned, the SST is not in the same class as the modern core bonded bullets, the 160 grain Nosler Partition or Barnes bullets. Nevertheless, wounding can be considered as to be so severe that almost always, where angling shots have been taken that have failed to reach vitals, medium weight game succumb quickly to massive internal trauma. Death can be delayed even though the animal has been anchored and while the nervous system and pain receptors may be destroyed, fast follow up shots, regardless of meat damage, are imperative for the sake of the quarry. 
 
As has been stated in the 7x57 text, the 162 grain A-Max will on lighter medium game, produce much faster killing at low velocities than the 162 grain SST where shots do not strike major bone. Unfortunately, on heavy bodied medium game, the A-Max is prone to suffer from shallow penetration when used at very close ranges. Wounds do extend through vitals however killing can be slightly delayed in these instances. The A-Max can be used to good effect in the Magnums at close ranges on heavy bodied medium game providing the hunter has realistic expectations of bullet limitations, utilizing suitable shot placement, exploiting the strengths of this inherently explosive bullet design. The A-Max is an extremely useful and satisfying hunting bullet, its strengths far outweigh its limitations. For very large bodied medium game at long ranges, the thicker jacketed SST can be used to great effect out at ranges as far as and exceeding 1000 yards.
 
Speer produce two very useful projectiles for the 7mm Weatherby, the 160 grain Hotcor and 160 grain BTSP. The 160 grain Hotcor is a little too stout for use on light bodied game and is best suited to game weighing between 80 and 200kg (180-440lb). The Hotcor is well suited to close range work where raking shots are to be expected, maintaining wide wounding out to a range of around 400 yards - providing enough resistance is met at the target to optimize bullet expansion.
 
The Speer 160 grain BTSP is a highly frangible bullet, suitable for light bodied game at close ranges and medium bodied game at longer ranges. Performance is very much like the 162 grain A-Max and the only major difference between the two designs is the BC, the Speer having a BC of .519 as opposed to .625 for the A-Max. Loaded to 3200fps, the Speer BTSP slows down to 2900fps (ideal for fast killing versus adequate penetration) at 150 yards and stays above 2000fps out to 700 yards. Beyond 700 yards, wounding is relative to target resistance such as bone and heavy muscle.
 
The Nosler 160 grain Partition is simply dynamite when driven at 3200fps. Few projectiles achieve such spectacular killing performance on medium game. The Partition design is pushed to its limits when driven at Weatherby velocities so hunters should not expect miracles with regard to penetration on large, heavy bodied animals at close ranges. The popularity of the 7mm Magnums has seen the Partition used on quite large, heavy bodied game over the last 20 years. In truth, the .30 caliber and medium bores place less strain on projectiles. When the Partition is used on game larger than 320kg (700lb), wound channels are narrow and 50% of bullets will suffer jacket base core separation. The 160 grain Partition is a good light through to medium weight game bullet and should be used accordingly. The Partition generally produces full expansion at 2200fps (500 yards) and on solidly built medium game, will more often than not, produce excellent (sometimes violent) wounding out as far as 650 yards (2000fps), quite a feat for an old fashioned bullet design with a BC of .475. 
 
The Nosler 160 grain Accubond is reliable medium game bullet.  Due to its core bonded design, wounding is much less violent than the Partition design however killing performance is excellent. The major difference between the Accubond and InterBond/Scirocco projectiles is that the Accubond sheds some frontal area.  This slight loss of the frontal core allows the projectile to swage into a more desirable form for deep penetration (the InterBond must be annealed to achieve this form) while also ensuring energy transfer on game of all body weights. The Accubond has a BC of .531, good for intermediate long range hunting however the core bonding limits expansion beyond 450 yards (2400fps). A few long range hunters use the Accubond out to 1000 yards however rear lung shots on light bodied game produce immensely slow kills.  The Accubond should really only be used on stout bodied medium game beyond 450 yards.
 
Swift’s medium weight 150 grain Swift Scirocco is a violent performer. Like the 139 grain InterBond and 140 grain Accubond, this projectile is better suited to hunting ranges inside 400 yards than for true long range hunting. At close to moderate ranges, the Scirocco meets its limits on game weighing 120kg (220lb) although on Boar, practical limits are 80kg (180lb).
 
The 168 grain Berger VLD is an acceptable performer in the Weatherby. Its only limitation is at close ranges on heavily bodied medium game. In such instances, bullet blow up can occur a little too early, resulting in wide yet shallow penetration. On inspection of kills, entry wounds through ribs can be as wide as five inches and one has to wonder how any mammal could escape such trauma. Lung wounding is usually adequate yet inexplicably delayed. Negative results are more pronounced when hunting steep terrain (cliff/ mountain bluff systems) when, rather than the anticipated long range shot, an animal presents itself at close range, the shot is taken, the animal runs then expires when traversing an escape route along a precipice never to be seen again. In flat open country where game are easily recovered, this slight delay in killing is not such a problem. On light bodied game, the 168 grain VLD is incredibly fast killing out to ranges of around 850 yards. Exit wounds at intermediate ranges (especially between 500 and 700 yards) are sometimes wider than 3”.
 
The Berger 180 grain VLD is one of the very best projectiles available for use in the Weatherby. This and the 162 grain SST are pretty much the ‘go to’ bullets for a wide range of medium game. Some rifles may not shoot this projectile accurately due to barrel twist rate versus individual barrel preferences however for those who wish to indulge in long range hunting, the 180 grain VLD deserves testing. Even though this is a long stable projectile, it is highly frangible. When using the VLD, the hunter must adopt the mindset that bullet blow up is desirable, not a negative factor. Penetration is purely relative to SD x fragmentation, the longer the bullet, the more gradual the fragmentation. This is not a bullet for tail on shots at close range although in truth, wounds are so wide on medium game that arterial bleeding often results in relatively fast killing. The 180 grain VLD is suitable for a wide range of game up to 200kg (440lb) but is not quite as effective on larger bodied game at close to moderate ranges as, for example, the 210 grain .30 cal VLD.   On medium game, performance decreases at impact velocities below 2000fps (800 yards) if only light resistance is encountered (rear lung shots).
 

Closing Comments

The 7mm Weatherby has made a comeback in recent years due to the popularity of long range hunting.  While this cartridge produces as much velocity as a 7mm bore can take without excessive erosion, the long free bore can sometimes limit versatility, some projectiles give excellent accuracy, some will not. Weatherby factory ammunition utilizes bullet designs that on average, produce desirable accuracy across the board. For hand loaders, experimentation is the key.

The Weatherby is a fast killing, highly effective medium cartridge. Recoil is somewhat sharp and in lieu of heavy barrels or muzzle brakes, requires a level of discipline with regard to handhold tensions and general shooting habits. As always, killing power is no substitute for poor accuracy. When both are combined, the results are spectacular.
 

Suggested loads: 7mm Weatherby Magnum					Barrel length: 26”
No	ID		Sectional Density	Ballistic Coefficient	Observed  MV Fps	ME Ft-lb’s
1	FL	Wby 160gr Partition	.283	.475	3200	3637
2	HL	139gr Interbond (AB)	.246	.486	3400	3567
3	HL	154gr SST/IB	.273	.525	3250	3611
4	HL	162gr SST	.287	.550	3200	3683
5	HL	162gr A-Max	.287	.625	3200	3683

 
 

Suggested sight settings and bullet paths
1	Yards	100	155	299	341	375	400	425	450
	Bt. path	+3	+3.9	0	-6	-6.2	-9	-12.1	-15.6
2	Yards	100	180	326	369	400	425	450	475
	Bt. path	+3	+4.2	0	-3	-5.8	-8.4	-11.3	-14.6
3	Yards	100	175	310	353	375	400	425	450
	Bt. path	+3	+4.1	0	-3	-5	7.5	-10.4	-13.6
4	Yards	100	170	305	347	375	400	425	450
	Bt. path	+3	+4	0	-3	-5.5	-8.1	-11	-14.3
5	Yards	100	170	309	352	375	400	425	450
	Bt. path	+3	+4	0	-3	-5	-7.5	-10.2	-13.4

 
 

No	At yards	10mphXwind	Velocity	Ft-lb’s
1	400	9	2417	2075
2	400	9	2600	2086
3	400	8.8	2528	2185
4	400	8.5	2516	2276
5	400	7.4	2592	2417

 
Note: Load No 1 duplicates hand loads. Load No 2 trajectory can be duplicated using 140gr Accubond.
 
 

 

	Imperial	Metric
A	.531	13.50
B	.521	13.00
C	R.151
D	.492	12.50
E	.310	7.87
F	2.06	52.51
G	.398	10.11
H	2.55	64.8
Max Case	2.55	64.8
Trim length	2.54	64.5

Discuss this article or ask a question on the forum here

Copyright © 2007-2011 Terminal Ballistics Research, Ballisticstudies.com