The .257, .270, 7mm And .300 Weatherby
Magnums Are Still Top Performers.
Roy Weatherby grew up during the Great Depression on a Kansas farm, in a family poor even for those days. After marrying in 1936, he moved to Southern California and ended up selling insurance, eventually making a yearly income of almost $100,000, adjusted to 2014 dollars. However, Weatherby was also an avid shooter, hunter and amateur gunsmith. Even during the shortages of World War II he developed some very fast big-game cartridges, a leap made possible by a new powder introduced in 1940, DuPont IMR 4350, by far the slowest-burning handloading powder then available.
The 7mm Weatherby (above) provides almost as much oomph as the .300, with considerably less recoil, even off the bench. This Mark V Ultra Lightweight in 7mm Weatherby Magnum (below) only weighs 8 pounds with scope, light enough for packing over elk mountains.
The first Weatherby wildcat was the .270 Weatherby Magnum, designed as an improvement over the popular .270 Winchester, the fastest factory big-game cartridge in America. The .270 Weatherby was made by shortening .300 H&H brass, then fire-forming the cases to increase powder capacity, with a distinctive double-radius shoulder that eventually said “Weatherby Magnum” like a gold ring says Leupold scopes. Within a year or two Weatherby also developed his .257 and 7mm Magnums on the same shortened case, and the .300 and .375 Weatherby Magnums, made by fire-forming the full-length .300 and .375 H&H cases in enlarged double-radius chambers.
The first Weatherby rifles were often rechamberings of factory rifles, one reason there are far fewer pre-’64 Model 70 Winchester .300 H&H’s than originally produced—and why some purchasers of pre’64 .300’s are still surprised when the first cartridge shot in their classic Winchester comes out of the chamber shaped differently. But soon Weatherby started offering custom rifles, sub-contracting the work he couldn’t do in his basement shop.
Many were stocked in what eventually became known as the California-style, often with hardwoods other than walnut, with exaggerated pistol grips and cheekpieces, flamboyant checkering and inlays of contrasting wood or even ivory. Roy Weatherby may not have been a master gunsmith, but he was a great promoter and realized many post-war hunters wanted something different than their father’s and grandfather’s rifles. Within a dozen years his company became successful enough to offer its own action, the Mark V, made by Sauer of Germany to Weatherby’s specifications. (Eventually Mark V’s were made in Japan, and today they’re made in the US.)
Of the five Weatherby Magnum cartridges offered in 1945, only the .375 is no longer chambered in any Weatherby rifle, mostly because it was surpassed in 1953 by the larger .378 Weatherby Magnum. The basic tenet of the company was to offer the highest velocity cartridge in any caliber, and the .378 is a belted variation of the .416 Rigby case, providing enough extra powder room for a 200 fps increase over the .375 Weatherby.
The other four original Weatherby Magnums, however, are all doing quite well. While their belted cases have gone out of style in some circles, there’s nothing fundamentally wrong with belted brass as long as handloaders understand fired cases should be resized just enough to chamber easily, preventing case stretching. The Weatherby rounds make this a little easier than conventional belted rounds, because the double radius essentially results in about a 40-degree shoulder angle, also reducing case stretching.
The biggest difference in handloading for the “old four” Weatherby rounds and most other rifle cartridges is the so-called freebore of their chambers, essentially an extra-long throat. Roy Weatherby discovered freebore reduced the steepness of the pressure curve, allowing more powder to be loaded for extra velocity. Essentially it works like using an even slower powder, increasing the “area under the curve.”
As a result, all four rounds can safely produce more velocity than conventional cartridges of the same powder capacity. This is most obvious with the 7mm Weatherby Magnum, a cartridge with almost exactly the same powder capacity as the 7mm Remington Magnum. In the Weatherby round another 100+ fps is possible, without any increase in pressure.
However, in Weatherby rifles the freebore is so long bullets can’t be seated out far enough to touch the rifling and still allow cartridges to fit in the magazine. This runs contrary to the belief that bullets must start close to the lands to shoot accurately, but freebore works fine as long as the extended throat is just slightly above bullet diameter, preventing bullets from tilting before they hit the rifling. In the past decade I’ve handloaded for factory Weatherby rifles in all four chamberings, and all have shot very well.
The four original Weatherby Magnums still chambered in
Weatherby rifles are (left to right) the .257, .270, 7mm and .300.
One other minor difference in the .257 and 7mm Weatherby Magnums is slower-than-normal rifling twists. The original .257 Weatherby rifles had 1:12-inch twists, perhaps because Roy Weatherby favored 100-grain bullets in his favorite cartridge. This resulted in the original “heavy” bullet factory load featuring the roundnosed 117-grain Hornady, since 117- to 120-grain spitzers wouldn’t stabilize. The twist was changed to 1:10-inch years ago, but Weatherby still offers 117-grain roundnose factory ammo for older rifles.
Many 7mm Weatherby rifles have 1:10-inch twists today, when the standard for other 7mm rifles has been around 1:9-inch ever since the 7×57 was born in 1892. While a 1:10-inch twist will stabilize any conventional hunting bullet, it won’t stabilize some of today’s ultra-long bullets with very high ballistic coefficients. As any example, the new 7mm Weatherby used in the handload tests, my own Mark V Ultra Lightweight, won’t stabilize the 168-grain Berger Hunting VLD. This is not big deal to me, since I mostly use 160-grain Nosler Partitions, which shoot very accurately.
With freebored Weatherby rounds it’s easiest to start with bullets seated so the cartridges just fit in the magazine. After working up the most accurate load possible, further experimenting can be done by seating the bullets progressively deeper. (In modern rifle cartridges using progressive-burning powders, pressure drops with deeper-seated bullets—or at least it does until bullets are seated extremely deeply.) This also goes against common belief, but many of today’s bullets shoot more accurately when seated deeper, especially “monolithics” without lead cores. In fact this happened with 130-grain Nosler E-Tips in the .270 Weatherby rifle, as shown in the loading data.
While the .300 Weatherby is extremely effective, I eventually grew weary of the recoil (a common affliction among shooters of a certain age) and these days prefer the smaller rounds. The .257 works particularly well on deer-sized game, though it’s also an effective elk round, and I know a sheep-ranching family in Wyoming that prefers it over any other round for coyote control. The .270 and 7mm Weatherbys are both great all-around big-game rounds, with a slight edge going to the 7mm because of the many 160- to 175-grain bullets available.
All of the bullets listed have worked well on various animals. The 7mm 120-grain Nosler Ballistic is mostly jacket, so works almost like a monolithic bullet, and the Hornady InterLocks and Sierra GameKings in heavier weights also work. In Colorado a few years ago my hunting partner took a 5-point bull elk with a single 175-grain Hornady InterLock from his 7mm Weatherby, and it performed perfectly.
While Weatherby still offers traditionally-styled Mark V’s in all four chamberings (here “traditionally” means California-style), both Vanguards and Mark V’s are also available in a vast array of 21st-century variations, including laser-etched walnut and interestingly painted synthetics. But they still fire the same great cartridges Roy Weatherby developed in his basement workshop.
Four of John Barsness’s nine books are on firearms and shooting. His latest, Rifle Trouble-Shooting and Handloading, was published in 2012 by Deep Creek Press, and is available through www.riflesandrecipes.com, P.O. Box 579, Townsend, MT 59644-0579, (406) 521-0273.
By John Barsness
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