Americans have loved .30 caliber rifle cartridges since the 1890s when Winchester released the .30-30 Win. And when Americans love a thing, they’re driven to improve it. That’s the story of Roy Weatherby and the 300 Weatherby Magnum.
While the Brits invented the magnum rifle cartridge, Weatherby strove to perfect it in .30 caliber form. Building on their work, he infused it with the American spirit to create a high-velocity rifle cartridge decades ahead of its time.
The 300 Weatherby Magnum is a rifle cartridge that performs at long range, spurring the future of cartridge design toward nasty .30 caliber speed. It came from the mind of a man who wasn’t afraid to think differently.
Roy Weatherby, Visionary and Innovator
“The big thing is to use modern, slow-burning powder and to shape your case to the burning characteristics of the powder,” Roy Weatherby said in a 1956 interview for Sports Illustrated called “The One-Shot Killer.” He was explaining his philosophy on cartridges.
“You can get power in a rifle pretty much the way you get power in an automobile. The more gas, the more power. Well, in bullets, the more powder, the more power.”
Those two quotes nicely sum up Roy Weatherby’s approach to cartridge development. When everyone else was preaching heavy and slow rounds, he was a heretic offering a counter gospel of light and fast. Velocity was king in his eyes. He sought to develop high-velocity, flat-shooting cartridges that buck the wind and hit hard. Some firearms experts say he was 50 years ahead of his time.
Weatherby mentions taking some friends on a Utah deer hunt in 1943. Those friends all shot a rifle chambered for his rounds. Weatherby commented, “…when they shot a deer with my rifle, the deer dropped like lightning no matter where they were hit.”
He was describing hydraulic shock, or what he called hydrostatic shock. The thought is that the pressure changes from the velocity create a shockwave that expands through the animal, increasing damage away from the entry point. The higher the velocity, the higher the shock. Weatherby wanted speed.
The rifle on that hunt in 1943 was chambered for a wildcat round Weatherby developed based on the .270 Win. It became the .270 Weatherby Magnum. Then it was on to .30 caliber rifles. A year later, he developed the .300 Weatherby Magnum.
300 Weatherby Magnum: Lineage of a .30 Caliber Wildcat
You know legendary English gunmakers Holland & Holland. If not directly, you know their famous cartridge, the .375 H&H Magnum. It’s the most popular bolt action cartridge for African, dangerous game.
Robert Ruark wielded his during the 1952 safari that produced his classic journal gone treatise on African hunting, Horn of the Hunter. He downed a lion, an eland, and a kudu with his .375.
In 1925, Holland & Holland necked down the .375 to hold a .30 caliber bullet, birthing the .300 H&H Magnum. At the time, it was the nastiest .30 caliber on the planet, hitting muzzle velocities over 3,200 fps with 150-grain projectiles. Holland & Holland released the patent rights to the .300 H&H Magnum in the late 1920s. But it still lived in obscurity.
Then, in 1935, a shooter named Ben Comfort won the 1,000-yard Wimbledon Cup with a .300 H&H Magnum built by Griffin & Howe. After that, the cartridge spread across America. Winchester began chambering the Model 70 in .300 H&H Magnum in 1937.
Roy Weatherby got his mitts on the .300 H&H Magnum, and in 1944 he improved it for more velocity, for that hot, nasty, hydrostatic shock-causing speed. He blew out the case for maximum powder capacity and re-engineered the shoulder to his signature double-radius design. Let’s talk in-depth about the specifics of the cartridge.
Remember Weatherby’s gas tank analogy, “The more gas, the more power… the more powder, the more power.” Weatherby increased the size of the gas tank (case) to give it more gas (powder). He did this by removing the taper of the .300 H&H magnum case. The result was a case of 91.5 grains of water, whereas the .300 H&H held only 85 grains of water.
The type of powder also matters. Holland & Holland charged the original .300 H&H Magnum with cordite, a now archaic smokeless powder. (Fun fact: Oppenheimer and the boys loaded Fat Man and Little Boy with cordite.)
Weatherby, however, used modern, slow-burning powder in his cartridge. The results were killer; we’ll discuss them in the performance and ballistics section. First, we have to touch on Weatherby’s signature shoulder design.
Weatherby maintained a max case length of 2.825 inches and built rifles with full-length magnum actions. Also, headspaced the chamber from the belt as the good folks at Holland & Holland did with their magnum cartridges. But as he straightened the taper of the .300 H&H case, he also rounded the shoulder into his signature double-radius or double-taper design.
Weatherby claimed that his shoulder design takes more advantage of the Venturi effect, a concept from fluid dynamics demonstrating that velocity increases and pressure decreases when gases flow from a less-constricted to more constricted space.
It’s proposed that Weatherby’s change in shoulder angle allows for more case pressure while also increasing the velocity of the gas through the neck of the cartridge after powder ignition.
Rifle aficionados have debated the Weatherby double-radius shoulder for the better part of a century. Some folks swear the rounded shoulder does what Weatherby said it does.
Others say it’s a marketing gimmick that forced people to come to him for ammunition and gunsmithing. The firearms community still hasn’t reached a definitive conclusion.
However, we do know that Norma loaded Weatherby ammo for a long time, and Swedish pressure standards are higher than American standards. But that’s no longer the case. Weatherby ammo is now loaded onsite in Sheridan, Wyoming.
Performance and Ballistics: How’s it Shoot?
The 300 Weatherby Magnum does what Roy Weatherby designed it to do, shoot fast and flat, even with heavy bullets. Weatherby’s current ballistics chart lists 12 rounds for the .300 Weatherby Magnum, starting at a bullet weight of 165 grains and progressing up to 200 grains.
According to the chart, a 165-grain Hornady Interlock leaves the muzzle at 3390 feet per second, carrying 1,769 ft.-lbs. of energy out to 500 yards with 23 inches of drop at that distance.
The last round on the chart is loaded with a 200-grain Nosler Accubond. That puppy leaves the barrel at 3,075 feet per second and carries 2,364 foot-pounds of energy out to 500 yards with 24 inches of drop. They calculate the drop from a 300-yard zero.
Roy Weatherby understood that velocity and kinetic energy matter for hydrostatic shock. It’s commonly accepted that 1,500-foot pounds is the minimum kinetic energy necessary to kill an elk.
If the current Weatherby ballistics chart reads true, every factory round for the .300 on their menu carries enough down-range energy to kill an elk beyond 500 yards.
That’s a nice bit of insurance if you’re a decent shot and you need to take a poke on big game. But even with shooting fast and flat, bullet construction matters. If you’re shooting far, you want a frangible bullet with a good B/C to buck wind and create nasty wound channels.
Speaking of B/C, what about windrift with the 300 Weatherby Magnum compared to other .30 caliber rounds? Bullet B/C matters, but on average it bucks wind better than most .30 caliber cartridges. Combine kinetic energy with wind deflection, and the 300 Weatherby Magnum shakes out to be a solid long-range hunting cartridge.
It’s important to note barrel length and construction. Weatherby traditionally constructed barrels with a longer throat, meaning there is more free bore or distance between the chamber and where the rifling starts.
The logic is that this increases velocity because the bullet has to “jump” to contact the lands. Some say this is important, while others say the velocity increase is negligible. Weatherby also manufactures and tests their .300 Magnum with a 26-inch barrel with a 1:10 twist.
Barrel length is critical for performance with magnum cartridges. Cut two inches from the barrel, and velocity could drop by hundreds of feet per second.
Competition for Speed
Weatherby designed the .30-378 Weatherby Magnumn in 1959 in response to a military contract. The folks in uniform were experimenting with sniper rounds. Weatherby necked down their .378 Weatherby Magnum cartridge to hold a .30 caliber bullet, and the result was a whole lot of case capacity and a whole lot of velocity.
Roy Weatherby never brought the .30-378 to market, but his son did in 1996. According to the ballistics chart on the Weatherby website, the .30-378 muzzle velocity with a 220-grain Nosler Accubond (the heaviest bullet listed) is 3050 feet per second.
The drop at 500 yards is 23.6 inches, comparable to the drop of a 165-grain bullet fired from the 300 Weatherby Magnum.
The .30-378 beat the .300 in speed, but it also added a nasty amount of recoil that most hunters don’t want. So, while the Weatherbys beat themselves with speed, they didn’t beat themselves in the market. Winchester, however, gave them market competition.
In 1963, Winchester released the .300 Win Mag. They manufactured it with a shorter receiver based on the .30-06 Sprg instead of the full-length magnum action. With that, the .30 caliber magnum cartridge became an approachable option for everyday folks.
The guns weren’t as expensive, and the shorter receiver, as well as headspacing off of the shoulder, made for easier ammo manufacturing. Instead of having to go directly to Weatherby as folks did for 300 Weatherby Magnum ammo, folks could pick up .300 Win Mag ammo from multiple manufacturers.
The .300 Win Mag doesn’t shoot as fast or as flat as the .300 Weatherby, but many hunters don’t care. It carries plenty of wallop, and the reduced velocity increases barrel life while reducing recoil. And when you cut a 300 Weatherby Magnum barrel down to 24 inches, the ballistic gap between it and the .300 Win Mag closes considerably.
The good folks at Remington released the .300 Remington Ultra Mag (RUM) in 1999. Rather than working from the .375 case as Weatherby did, they necked down a .404 Jeffries case to hold a .30 caliber bullet.
At 110.2 grains of water, the .300 RUM bests the case capacity of the 300 Weatherby Magnum by about 15 percent, giving the .300 RUM higher velocity potential.
The case is also unbelted and headspaced from the shoulder, which typically extends case life; that’s important for handloaders, which is where the .300 RUM surpasses the 300 Weatherby Magnum.
Their ballistics are similar with factory ammo, but the increased case capacity and longer case life sets the .300 RUM apart from the .300 Weatherby in the case of performance potential and cost to shoot.
Regardless of the competition, Roy Weatherby created a high-performing rifle cartridge ahead of its time.
The 300 Weatherby Magnum, A Cartridge Ahead of its Time
When everyone else was thinking about heavy, slow rifle rounds, Roy Weatherby thought about speed. His innovative mindset drove him to create the 300 Weatherby Magnum, a cartridge at the top of the .30 caliber performance list for nearly 80 years, despite emerging competition.
It shoots fast, flat, and carries energy down range, delivering shocking power to whatever critter it hits.
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