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Weatherby's .30-Caliber Power Pair

Loaded with 180-grain hunting bullets, the .300 Weatherby Magnum and .30-378 Weatherby Magnum achieve whopping velocities ranging from 3,120 fps to 3,330 fps.

Weatherby's .30-Caliber Power Pair

The .300 Weatherby Magnum (left) and the .30-378 Weatherby Magnum (center) are a real power duo compared to other .30-caliber Magnums like the .300 H&H Magnum (right). (Shooting Times photo)

Roy Weatherby knew how to get attention.

When I was a kid, “Weatherby” meant “power.” For .30-caliber fans, Weatherby created two powerhouses: the .300 Weatherby Magnum and the .30-378 Weatherby Magnum.

The .300 Wby. Mag. (1945) was among Roy’s early offerings of proprietary cartridges based on the Holland & Holland belted case. Those under .30 caliber were built on a shortened H&H case for .30-06-class actions. The .300 upped the game by using the H&H case at full length.

The .300 Wby. Mag. was a barn-burner. In an old compendium of advertised specs for contemporary .30-caliber rifle cartridges with 180-grain bullets, the .30-06’s nominal was 2,700 fps, and the .300 H&H was listed at 2,920 fps. The same source shows the .300 Wby. Mag. at 3,245 fps. Current Weatherby specs show similar velocities.


In 1994 the .300 Wby. Mag. was among the first Weatherby cartridges to be standardized by SAAMI. Prior to those standards, we tested with secondary methods that took much longer.


For Speer Reloading Manual #13 we had new transducer pressure barrels, updated standards, and calibration ammunition. The industry maximum average pressure (MAP) is set at 65,000 psi.

The higher resolution afforded by transducer testing showed us that not all propellants were appropriate to lighter bullets in that big case. We let extreme variation of pressure guide our propellant choices with bullets lighter than 150 grains.

As with any big case, the .300 Wby. Mag. posts best ballistic uniformity with 180- and 200-grain bullets, and that is where its strengths lie. Today’s lower-drag hunting bullets are capable of delivering its energy at long ranges, and it remains a great cartridge for hunting in the West.

As the name implies, the .30-378 Weatherby Magnum derives from the older .378 Weatherby (1955), giving a massive capacity that is 14 percent greater (water) than the .300 Remington Ultra Mag and 30 percent greater than the .300 Wby. Mag. It was developed in 1959 but wasn’t released commercially until 1996.




Two narratives say it was a response to a military request. One describes a long-range target cartridge for military rifle teams. However, the description on Weatherby’s website says it was requested for the Redstone Arsenal and “…loads were to be developed to exceed 4,000 fps and close to 5,000 fps.”

The Redstone narrative makes more sense. The Redstone Arsenal in Huntsville, Alabama, was central to U.S. rocket research in 1959. Those crazy velocity specs suggest it was needed for researching hyper-velocity microparticle effects.

Capable of launching a 220-grain bullet at nearly 3,100 fps, the .30-378 should stay supersonic at 1,000 yards with the right bullet. Advertised factory ammo velocities are a 165-grain bullet at 3,500 fps, 180-grain bullet at 3,420 fps, and 200-grain bullet at 3,160 fps. Crusher MAP is 55,100 CUP.


SAAMI reference ammunition for pressure-barrel calibration was unavailable when we tested the .30-378 for Speer Reloading Manual #14. We requested secondary reference ammo with the factory’s lot-assessed pressure. The first samples, with 165-grain bullets, posted pressures in our test barrel well under the values provided, making for some questionable results at our end. We started over.

My fellow ballistician and friend, the late George Weber from Hodgdon, suggested we ask for assessed samples loaded with the heaviest bullet offered. We subsequently received some 200-grain ammo that our barrel shot virtually the same average pressure as Weatherby’s assessment. We completed testing the big .30 with no further issues thanks to George’s experiences with secondary reference ammo. I miss our chats, my friend.

It shouldn’t be surprising that the best ballistics consistency in this massive case is with bullets 180 grains and heavier. Bullet construction is vital. A conventional 150-grain SP can achieve 3,600 fps but will disrupt like a varmint bullet on big game. Use tough bullets.

The .30-Caliber Horserace

I look to the 180-grain bullet when comparing .30-caliber cartridges for .30-06 on up. I think it is the best weight for game in this class of cartridges.

Any velocity comparison brings up the issue of barrel length. The standard U.S. industry rifle test barrel is 24 inches. Weatherby selected a 26-inch barrel as its velocity standard years before the company was a SAAMI member because that was the length of its production barrels. That’s fine, but I needed a common platform for judging safe max velocities. To me, that is the industry-standard, calibrated, 24-inch pressure-velocity test barrel, posting actual—not advertised—velocities from the best propellants available to handloaders.

Can that two inches make a difference? Generally, reductions of 25 to 40 fps per inch of barrel removed have been my “guesstimator.” The .30-378 sample Weatherby supplied us, with a 200-grain Partition, is advertised at 3,160 fps (26-inch barrel). It posted a 10-shot average of 3,081 fps from our 24-inch pressure-velocity barrel. That’s a change of 40 fps per inch.

I sought the highest velocity 180-grain loads published for all active .30-caliber Magnums SAAMI lists with .300 H&H propellant capacities and larger. Data came from Hodgdon and Speer who used 24-inch industry barrels.

The .30-378 leads the pack at 3,334 fps. The next is the .300 RUM, with a mass of loads clustering in the 3,150 to 3,225 fps range. A single Hodgdon load posted a sizzling 3,300 fps. That is a statistical tie unless we toss that data point. If tossed, that puts the .300 RUM in second place—barely. The next slot gets interesting.

Hodgdon has 30 Nosler data at 3,128 fps; Speer has data for the .300 Wby. Mag. at 3,122 fps. Another dead heat, except Hodgdon lists several propellants for 180-grain bullets in the .300 Wby. Mag. that outpace the 30 Nosler, with velocities up to 3,171 fps. The .300 Wby. Mag. is third whether or not the .30-378 and the .300 RUM are tied.

So, the .300 Wby. Mag., a cartridge that first “burned barns” 75 years ago, is far more than just “relevant” today. In spite of my preference for non-belted cases, the .300 Weatherby Magnum, with its history, great performance, and that long reloader’s neck, still sings a siren song to me.

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