Compared: The .270 WSM and .270 Weatherby Magnum
By Chuck Hawks
The .270 WSM, introduced in 2002, is perhaps the most useful and may, in the long run, be the most successful of the WSM and WSSM cartridges. For the very rare hunter with the skill to take advantage of a trajectory even flatter than that offered by the standard .270 Winchester, the .270 WSM offers that capability in a short (.308 length) action rifle. The .270 WSM was introduced in the Browning A-Bolt II and Winchester Model 70 rifles, and has since been picked-up by other manufacturers. Winchester Model 70 rifles in .270 WSM caliber are supplied with 24" barrels; Browning A-Bolt II models are supplied with 23" barrels.
The .270 WSM is based on a necked-down .300 WSM case, which is loosely based on a severely shortened, sharp shouldered version the very large .404 Jeffery case. The short, very fat, .270 WSM case has a (.530") rebated rim to allow it to mate with standard magnum diameter bolt faces. Like the .404 Jeffery and the other WSM calibers, but unlike most previous magnum cartridges, the .270 WSM case is beltless. The SAAMI maximum average pressure (MAP) for the .270 WSM is pegged at 52,000 cup.
At the time of this writing .270 WSM ammunition is factory loaded only by Winchester. I imagine that other ammunition manufacturers will load .270 WSM ammunition in the future.
Winchester offers two .270 WSM factory loads in their premium priced Supreme line. The first of these drives a 130 grain Ballistic Silvertip bullet (a moly-coated version of the Nosler Ballistic Tip) at a muzzle velocity (MV) of 3275 fps with 3096 ft. lbs. of muzzle energy (ME). The second drives a 140 grain Fail Safe bullet at a MV of 3125 fps with 3035 ft. lbs. of ME.
Winchester also offers a .270 WSM factory load in their standard Super-X line. This load features a 150 grain Power Point bullet at a claimed MV of 3150 fps with 3304 ft. lbs. of ME. All Winchester .270 WSM ballistics were developed in 24" test barrels.
Winchester rates the 130 grain Supreme and 150 grain Super-X loads as best for CXP2 class game (deer, antelope, sheep, goats, and black bear). The 140 grain Supreme load is rated CXP3 (large, heavy game).
The .270 Weatherby Magnum has offered ultra-long range shooters similar capability since 1943. The .270 was Roy Weatherby's first commercial cartridge design, and one of his best and most popular. It is a standard (.30-06) length belted magnum based on a shortened, blown out, and necked down .300 H&H Magnum case. The SAAMI maximum average pressure for the .270 Weatherby Magnum is 53,500 cup.
The .270 Magnum is currently offered in a number of Weatherby Mark V rifle models, and has also been chambered in the Ruger No. 1 single shot rifle and the Winchester Model 70 bolt action rifle. Current Weatherby rifles in .270 Wby. Mag. caliber come with 26" barrels.
Factory loaded .270 Weatherby Magnum ammunition is available from Weatherby and Federal. Norma of Sweden, who manufactures Weatherby brand ammunition to Weatherby specification, is said to be planning to market the Weatherby calibers under its own name.
The premium Weatherby ammunition line offers the greatest variety of .270 Magnum loads. These include a 100 grain bullet for shooting varmints and small predators, plus two 130 grain bullets, two 140 grain bullets, and two 150 grain bullets suitable for big game hunting.
The 130 grain bullets are the Hornady SP Interlock and Nosler Partition, both at a MV of 3375 fps and ME of 3288 ft. lbs. The first 140 grain bullet is a Nosler Ballistic Tip at a MV of 3300 fps and ME of 3385 ft. lbs. The second 140 grain bullet is a Barnes-X at a MV of 3250 fps and ME of 3283 ft. lbs. The 150 grain bullets are the Hornady SP Interlock and the Nosler Partition, both at a MV of 3245 fps and ME of 3507 ft. lbs. All Weatherby .270 Magnum ballistics were developed in 26" test barrels.
At .270 Weatherby velocities the Hornady Interlock and Nosler Ballistic Tip bullets are probably best used on CXP2 class game such as antelope, deer, sheep, goats, feral pigs, and black bear. The premium Barnes-X and Nosler Partition bullets are an excellent choice for CXP3 class large game such as caribou, elk and moose.
Winchester promotional material for the .270 WSM has stated that, "The new .270 WSM elevates the .270 Winchester performance to a whole new level not previously available. Fans of the .270 now have a flatter, longer range, harder hitting hunting favorite."
If we examine that statement we find that it is at least half true. Compared to the standard .270 Winchester, a fine hunting cartridge in its own right, the .270 WSM does provide a flatter trajectory and greater energy. But does this constitute a whole new level of performance? I think not. Winchester has been pretty coy about not mentioning the .270 Weatherby Magnum in their literature, and for good reason. The .270 Weatherby has been providing the same (or greater) benefits to .270 fans for some 59 years prior to the introduction of the .270 WSM!
Now let's see how these two hot .270 Magnums stack up. One nice thing is that both Winchester and Weatherby developed their factory load ballistics in the same length barrels actually supplied on their rifles, so no velocity correction is necessary when comparing the two calibers.
The .270 Weatherby Magnum has a 100 fps muzzle velocity advantage over the .270 WSM with 130 grain bullets. With 140 grain bullets the Weatherby MV advantage increases to 125-175 fps, depending on which Weatherby load is chosen. With 150 grain bullets, a weight that would seem to be ideal for a .270 Magnum rifle, the Weatherby caliber has a MV advantage of 95 fps.
It's a shame that Winchester .270 WSM rifles are not supplied with 26" barrels, which would probably gain 60-100 fps of MV over their 24" barrels. However, that would defeat the purpose of a short action magnum. Reality strikes again, there really is no free lunch.
That .270 WSM velocity deficit translates to an energy deficit. With 130 grain bullets this amounts to 192 ft. lbs. of muzzle energy. With 140 grain bullets the .270 WSM's energy deficit is 248-350 ft. lbs. And with 150 grain bullets the difference in ME is 203 ft. lbs. in favor of the .270 Weatherby.
Since both calibers handle bullets of equal weight, sectional density, frontal area, and performance, it is clear that the .270 Weatherby has more killing power than the .270 WSM. According to the "Maximum Optimal Ranges for Big Game" table, the maximum optimal range for the .270 WSM using a 130 grain bullet on 400 pound game animals is 320 yards; for the .270 Weatherby the maximum optimal range is 390 yards, a 70 yard advantage. Comparing 150 grain bullets, the maximum optimal range on 600 pound animals is 275 yards for the .270 WSM and 320 yards for the .270 Wby. Mag., an advantage of 45 yards for the latter.
Both the .270 WSM and the .270 Weatherby Magnum are long range or ultra-long range calibers, so a flat trajectory is presumably of considerable importance to fans of either caliber as well as potential buyers. The "Rifle Trajectory Table" shows that when both calibers are shooting identical 140 grain bullets (BC .456) at factory load velocities, their respective maximum point blank range (within which the bullet has a maximum rise and fall of no more than 3") looks like this:
The result is similar with 130 and 150 grain bullets. With full power loads the greater case capacity and higher MAP of the .270 Weatherby means that it will always offer higher performance in every category than the .270 WSM.
Of course, with higher ballistic performance comes increased recoil. The "Rifle Recoil Table" shows that, in scoped rifles of typical weight, the comparative free recoil energy looks like this:
Using full power loads in rifles of equal weight, the .270 WSM kicks less than the .270 Weatherby Magnum, period. However, there are a dearth of rifles of equal weight in these two calibers. While most .270 WSM rifles will weigh around 8 pounds when scoped, Weatherby offers .270 Magnum rifles of at least three different weights. The Accumark, Fibermark, Stainless Laminate, Euromark, Lazermark, and Deluxe all weigh 8.5 pounds (bare rifle). A few models weigh 8 pounds (bare rifle), and the Ultra Lightweight weighs only 6.75 pounds (bare rifle). It is customary to add one pound to account for the weight of a scope and mount. Thus the most common test weight of a .270 Weatherby Magnum rifle varies between 7.75 pounds and 9.5 pounds, with the latter weight probably being the most common. It is this extra, recoil reducing weight that makes a .270 Weatherby rifle reasonably comfortable to shoot.
It is worth mentioning that a major factor in perceived recoil (what the shooter feels) is the stock design. This is one area where Weatherby has a lot of experience, and it shows (or rather, can be felt). The Weatherby stock is well designed to minimize the recoil of calibers like the .270 Wby. Mag., and its effect on the shooter. Weatherby's experience with magnum rifle calibers also shows in their use of 26" barrels to maximize ballistic performance and the substantial, recoil moderating weight of most Weatherby models.
What can one conclude from the forgoing? For the shooter wanting the top performance in the caliber, the .270 Weatherby Magnum is clearly the way to go. Ditto the person who admires Weatherby rifles, for they don't chamber for the .270 WSM.
For the person who prefers Browning or Winchester rifles the .270 WSM will have to be chosen, as those companies do not chamber for the .270 Weatherby. Also, there is a better selection of other rifle brands and price points in .270 WSM caliber.
For the person who is recoil sensitive, it would be best to avoid both magnum calibers, as the practical difference in recoil is relatively minor and neither caliber is really pleasant to shoot. Both also generate substantial muzzle blast. A rifle for the standard .270 Winchester caliber would be a better choice, and Browning, Weatherby, and Winchester (as well as virtually all other rifle manufacturers) offer .270 Winchester caliber rifles in a plethora of models.
For those desiring more information, articles about both the .270 WSM and .270 Weatherby Magnum can be found on the Rifle Cartridge Page.
Copyright 2003, 2012 by Chuck Hawks. All rights reserved.