The .300 Weatherby Magnum

Developed by wildcatter Roy E. Weatherby in the mid-1940s, the .300 Weatherby Magnum was not the first of Roy’s fast wildcats, but it has remained the flagship of the line since Weatherby, Inc., went into production more than 60 years ago. It is also just about the only Weatherby magnum that has expanded from a Weatherby proprietary into general production. Not everybody offers it, but a number of firearms manufacturers chamber to it, and among the “majors,” Federal, Hornady, and Remington offer factory ammunition.  

The .300 Weatherby Magnum was created quite easily by removing the body taper from the .300 H&H case, thus significantly increasing powder capacity and resultant velocity. The nominal case length of 2.8 inches is retained, so we call the .300 Weatherby a “full-length” magnum, requiring a .375 H&H-length action and unable to fit into a standard or .30-06-length action. The .300 Weatherby Magnum was not the only “improved” version of the .300 H&H. 

There were several, using slightly different body tapers, shoulder angles and neck lengths; Roy Weatherby’s version used his distinctive double venturi curved shoulder—the only version that made it into factory form. My late uncle, Art Popham, long-time member of Boone and Crockett, was a friend of Roy Weatherby’s and, from the late ‘40s onward, did most of his hunting with a .300 Weatherby out of deference to Roy—but his rifle was actually a .300 Improved, with a different shoulder. 

Roy Weatherby’s theories were good, but he was also a master marketer. His version was faster than the rest, but it wasn’t exactly cartridge design. Early on, he partnered with the Swedish firm of Norma to load his ammo. Norma still loads Weatherby’s ammo—and loads it to slightly higher pressure than American standards. Weatherby also cut his chambers with a bit of “free bore”—an unrifled section ahead of the chamber, which allowed the bullet to get a jump-start before engaging the rifling. Even today, .300 Weatherby ammunition (from Norma) is considerably faster than the competition. I have found Weatherby’s published velocities, which are very high, to be pretty darned accurate in a Weatherby chamber with the specified barrel length (which is generally 26 inches, while the more customary industry standard is 24 inches). 

Weatherby’s published velocities include a 150-grain bullet at 3,540 fps, 165-grain bullet at 3,330, and 180-grain bullet at 3,250. Loads from other manufacturers (generally quoted from a 24-inch barrel) average about 150 fps slower. Honestly, I have found it difficult to handload up to Weatherby factory specifications, and in some non-Weatherby chambers there can be sticky extraction with Weatherby factory ammo, especially in hot weather.

This is hair-splitting—but necessary—discussion. After the 7mm Remington Magnum, the .300 Winchester Magnum is the world’s most popular magnum cartridge. It has the advantage of fitting into a .30-06-length case, but it is significantly slower than any loads for the .300 Weatherby Magnum—at least 150 fps slower. I have never been bothered by the slightly longer bolt throw and extra ounces of action weight. But, as the tradeoff, when I want a fast .30-caliber, I want all I can get! The .300 Weatherby Magnum isn’t a cartridge I use all the time, but I’ve owned at least one rifle so chambered since 1980, and I prefer it above all other fast .30s. 

It should be said, and I will admit, that the .300 Remington Ultra Mag (RUM), with its fatter, unbelted case, is a better cartridge. Its design is far more modern, and since it has greater case capacity it is theoretically faster. And with carefully worked up hand loads it could be, but factory ammunition is only available from Remington, so the .300 Weatherby Magnum is more available. If you wish to continue to split hairs over velocity, Remington’s .300 RUM factory ammo is not as fast as Norma’s .300 Weatherby Magnum ammo produced for Weatherby. 

For many years the .300 Winchester Magnum was damned for its short neck, but it has long proven itself a very accurate and efficient cartridge. The unbelted .300 RUM is probably inherently more accurate, and the .300 Winchester Short Magnum definitely is. On the other hand, nobody has ever said that the .300 Weatherby Magnum is a 1,000-yard match cartridge. 

A fast .30 like the .300 Weatherby isn’t essential for caribou, but the tundra is often windy, and long shots can be required. I used my Rifles, Inc., .300 Weatherby to take this beautiful Quebec-Labrador bull.

However, as a hunting cartridge I have never seen any accuracy issues with the .300 Weatherby Magnum, and it is my experience that quality of barrel and ammunition—and precision of assembly—are more important to accuracy than cartridge design. I have used several Weatherby factory rifles that provided fine accuracy, and for many years a favorite go-to rifle has been a Rifles, Inc., .300 Weatherby on a left-hand Model 70 action with 26-inch fluted barrel. This rifle groups well with everything I feed it, and on a good day with good ammo produces quarter-inch groups. More recently I’ve been using a .300 Weatherby Magnum barrel on a Blaser R8. It, too, shoots far better than I can! I haven’t used it much in North America yet, but I’ve used it on a number of mountain hunts in Europe and Asia. 

At the Safari Club convention, my booth was across the aisle from legendary riflesmith Kenny Jarrett. He talked me into a custom-built rifle, and of course he wanted it to be in his signature proprietary, the .300 Jarrett (another “improved” version of the .300 H&H). Yes, his cartridge would probably buy me a few thousandths in group size—especially in one of his rifles—but would also incur long-term costs in ammo availability. I agreed, but only if he would build me a .300 Weatherby Magnum. 

In the 1950s all Weatherby cartridges were damned for premature bullet blowup. With the bullets we had back then there was probably some validity; bullets designed for ideal performance at .30-06 velocities can still come apart at the .300 Weatherby’s much higher speed. But this is a passé argument. Today we have plenty of good, tough bullets that will hold up at .300 Weatherby velocities. I don’t choose the lightest, most volatile bullets, and I don’t worry about it. 

Like any fast .30, the .300 Weatherby Magnum is a great choice if you’re going into unfamiliar country where you don’t know what kind of shot you might be facing. It is probably more powerful than necessary for the majority of North American big game, and is marginal at best for the big bears. But it’s also a fine choice for non-dangerous game bigger than deer, such as elk and moose, and a wonderful choice for African plains game, which can run the gamut in size and shooting conditions. It has the wind-bucking ability of the fast .30, so it is never a bad choice in mountains or plains. I’ve used it on North American sheep as well as in the big mountains of Asia. After 30 years of using this cartridge, I know it. I understand the trajectory, and it has never let me down! 

During most of that time I’ve been a staunch 180-grain fan, although I’ve gone to 200- and even 220-grain bullets for specialized applications. Today, thanks to the great bullets we have available, there is rarely a reason to go above 180 grains in bullet weight. Loads vary tremendously, but you can count on a solid 3,100 fps in a 24-inch barrel. This is not possible in a .300 Winchester Magnum, and with certain loads in some rifles, you might get 3,200 or more. 

In recent years (once again, thanks to better bullets), I’ve actually stepped down, using 150- and 165-grain bullets for smaller-bodied game. While the lighter bullets with inferior ballistic coefficient don’t hold up as well at extreme range, they are considerably faster. So flight time—and the wind’s ability to work on the bullet—is reduced. At normal game ranges on smaller-bodied sheep and goats, good 150-grain bullets at up to 3,400 fps have performed like magic. 

With its belted case and Roy Weatherby’s just plain weird shoulder design, the .300 Weatherby Magnum is now an older cartridge of archaic design. But it works. And although I’ve used and admire all of them, the Weatherby remains my personal favorite among the versatile fast .30-calibers.