6.5-300 Weatherby Mag Load Data
August 19, 2019
It's no secret 6.5mm cartridges are the hot trend, so it shouldn't have been surprising when a Weatherby Magnum became the fastest 6.5 of all. Here's some 6.5-300 Weatherby Mag load data to get you started.
Roy Weatherby liked to design cartridges with more zip than other commercial rounds. While not all Weatherby Magnums are the velocity champions in their caliber, the 6.5-300 Weatherby Magnum beats all challengers. Its factory loads include the Barnes 127-grain LRX at a listed 3,531 fps, Swift 130-grain Scirocco II at 3,476 fps, and Swift 140-grain A-Frame at 3,395 fps.
It’s somewhat surprising, however, that it took so long for a 6.5mm Weatherby to appear, but then until relatively recently most American hunters thought 6.5s were a little weird. Many wondered what a 6.5 would do that an honest American caliber, such as the 270, wouldn’t. And that’s exactly why Roy Weatherby’s first Magnum was the 270 Weatherby Magnum. It provided a big velocity increase over the popular 270 Winchester round.
The 270 Winchester itself played a large role in the relatively slow sales of the first three American factory 6.5s: the 256 Newton, 264 Winchester Magnum, and 6.5 Remington Magnum. The 264 Win. Mag. was by far the most popular, though not for long. Introduced in 1958, it almost disappeared after 1962 when the 7mm Remington Magnum appeared, which, by some not-so-odd coincidence, is the 264 Win. Mag. necked up 0.02 inch. The 256 Newton died with Charles Newton’s rifle company, and the short, fat 6.5 Remington was pretty much dead on arrival when it appeared in 1966, long before short and fat became fashionable for rifle cartridges.
Back then most hunters considered bullet weight and muzzle velocity the major factors when selecting a big-game cartridge. Millennials may not believe this, but there weren’t any laser rangefinders in the 1960s, so most hunters didn’t shoot big game much beyond 400 yards. Beyond 400 yards any rifle bullet dropped so steeply that misjudging the range by a mere 50 yards often resulted in a miss—or worse: a wounded animal.
Also, the only American controlled-expansion bullet was the Nosler Partition, and aside from costing twice as much as cup-and-core bullets, only Weatherby offered Partitions in factory ammunition. That was smart on Weatherby’s part, but most hunters believed extra bullet weight was the only way to increase penetration on large animals. The 7mm Rem. Mag. buried the 264 Win. Mag. because its initial factory loads featured 150- and 175-grain bullets—and the 150’s listed muzzle velocity was 60 fps faster than the 3,200 fps of the 264’s 140-grain bullet.
By the 1980s a greater knowledge of premium bullets started to change hunters’ ideas about lighter bullets. A decade later the appearance of affordable, handheld laser rangefinders changed the game again. Range could be measured rather than “guesstimated,” and solid hits beyond 400 yards not only were possible, but in the right conditions, were relatively easy.
At that point, 6.5mm cartridges started gaining in popularity because more hunters were discovering what target shooters already knew: 6.5 spitzers have very high ballistic coefficients, especially for their relatively light weights. This isn’t due to some mysterious ballistic magic, but because so many 6.5 cartridges appeared in the 1890s as military rounds, during the transition from black powder to smokeless powder.
Early smokeless-powder military cartridges featured heavy roundnose bullets, apparently because heavy roundnose bullets were used in the black powder rounds they replaced. Faster rifling twists were required to stabilize the small-caliber bullets, and many early military 6.5mm cartridges used 155- to 160-grain bullets in a rifling twist of about one turn in eight inches.
Eventually, most armies switched to lighter spitzers, increasing range due to higher ballistic coefficients and faster muzzle velocities. Among them was Sweden, replacing the original 156-grain roundnose in its 6.5x55 with a 139-grain boattail spitzer, the heaviest that would reliably stabilize in the nominal 1:8.66-inch rifling twist, especially in the Scandinavian cold.
During that same period, bullets for commercial hunting rounds often weighed far less, due to the desire for higher muzzle velocity. As a result, calibers that didn’t originate for military use often had slower rifling twists. When Winchester introduced its then-new 270 cartridge in 1925, the twist was 1:10, which was not fast enough to stabilize spitzers with ballistic coefficients as high as the 6.5x55’s 139-grain boattail. That’s the reason 270s aren’t favored among today’s long-range hunters.
The highly efficient 139-grain load also transformed the relatively mild 6.5x55 into a very effective long-range cartridge. Back then most American target shooters believed heavier bullets drifted less in the wind, so they stuck with .30-caliber bullets for long-range target shooting. In fact, writer Elmer Keith, who punched plenty of competition targets in his younger days, predicted a big .33-caliber cartridge would prove most popular for 1,000-yard target shooting.
In reality, ballistic coefficient, not bullet weight, is the major factor in wind drift, and eventually American target shooters “discovered” the ballistic virtues of mild-recoiling 6.5mm cartridges. Soon 6.5s started taking over the hunting market as well.
Enter the 6.5-300 Weatherby Mag
While many hunters prefer smaller 6.5mm rounds due to their light kick, some prefer the old American tradition of having it all. Why not combine the virtues of sleek 6.5mm bullets with very high muzzle velocity? Rather than using the same 2.5-inch case as the 257, 270, and 7mm Weatherby Magnums, the 6.5-300 Weatherby is the 300 Weatherby necked down, hence its name. The 300 Weatherby originated as a blown-out, “improved” 300 Holland & Holland Magnum, so its case is about a third of an inch longer than the shorter Weatherby Magnums.
When Roy Weatherby developed his first magnums, the slowest-burning powder available to handloaders was IMR 4350, and it is far too fast burning for the 6.5-300. These days far slower powders exist, but the 6.5-300 is still somewhat “touchy” (the word used by Hodgdon’s Ron Reiber when he sent me the newly developed 6.5-300 loading data).
By coincidence, the only available 6.5-300 Mark V rifle that Weatherby had on hand for this project was an Ultra Lightweight with a slim, fluted barrel. Over the past 20 years I’ve achieved excellent accuracy with Weatherby rifles chambered for Weatherby Magnums from the 240 to the 300, including some Ultra Lightweights. But like the 6.5-300 itself, the slim-barreled Ultra Lightweight rifles have proven somewhat “touchy” about which loads they’ll shoot well.
With the 6.5-300, this touchiness was reduced by the quality of Weatherby cases and the excellent ammo produced by the Redding dies that I used. (Note that RCBS also has dies for the 6.5-300 Weatherby.) The 40 cases I used in this project were very consistent in weight and neck thickness, and the dies resulted in loaded rounds with at most 0.003-inch bullet runout, and this consistency resulted in repeatable groups.
Hodgdon’s data included loads for five bullets: the Barnes 127-grain LRX, Swift 130-grain Scirocco II, Swift 140-grain A-Frame, Nosler 142-grain AccuBond Long Range (ABLR), and Hornady 143-grain ELD-X. I had three of the five on my shelves, but I couldn’t come up with any 140-grain A-Frame or 142-grain ABLR bullets, so I substituted the Nosler 140-grain Partition.
Swift A-Frame bullets develop higher pressures than most other bullets of the same weight and diameter; this is probably due to their pure copper jackets. This is reflected in Hodgdon’s data, which lists higher maximum charges for the 142-grain ABLR and 143-grain ELD-X. Nosler Partitions also tend to produce higher pressures than some other bullets, and in the Ultra Lightweight rifle’s 26-inch barrel (the same length as Hodgdon’s test barrel), muzzle velocities ranged between those listed in Hodgdon’s data for 140-grain A-Frames and 142-grain ABLRs. Consequently, I regarded a powder charge about halfway between those listed for A-Frames and ABLRs as maximum.
Initially, all four bullets were seated to the overall cartridge length listed by Hodgdon (3.590 inches), and instead of trying every powder-and-bullet combination in Hodgdon’s data, I tried the three powders listed as providing the highest velocities with each bullet. After all, the major point of the 6.5-300 is velocity, so why use powders producing less velocity?
IMR 8133 Enduron for 6.5-300 Weatherby Mag Handloads
One of the powders listed as fastest with all bullet weights was IMR 8133, the newest and slowest-burning in the Enduron line of temperature-insensitive powders. Like all Enduron powders, IMR 8133 is a “short cut,” double-based, extruded powder that also includes a decoppering agent. The other Enduron powders have provided fine results in my rifles, and this new one also proved to be excellent, splitting the honors for the most accurate loads with Hodgdon US869 powder.
Somewhat oddly, during initial load workups, the Hornady 143-grain ELD-X was the only bullet that didn’t shoot sub-inch groups. The ELD-X in other calibers had grouped extremely well in several of my rifles, but I’ve sometimes found the long “freebore” throats of most Weatherby Magnums can also be kind of touchy with high-ballistic-coefficient boattail bullets. Often the problem can be solved by experimenting with seating depth, and seating the 143-grain ELD-X 0.04 inch deeper resulted in 0.75-inch groups. Since the magazine allowed seating bullets out to an overall cartridge length of 3.660 inches, I also tried some at that length, but the first group spread over 2 inches. Many handloaders assume seating bullets closer to the lands results in finer accuracy, but that’s not always true.
The Nosler 140-grain Partition provided the best overall accuracy of any of the four bullets. Many handloaders would consider that odd, but it didn’t surprise me. I’ve rarely encountered any trouble getting them to shoot sub-inch groups at 100 yards despite the fact that they are not target bullets. When they don’t, the problem often can be solved by following the advice of Gail Root, the former bullet designer for Nosler, who suggested switching to a slightly faster-burning powder. He believed the rear core was “bumped up” slightly in diameter by quicker powders or more pressure, resulting in Partitions fitting the bore a little tighter. I’ve also found Partitions often shoot better with maximum loads, probably for the same reason.
I’ve also often found 140-grain 6.5mm bullets to shoot more accurately than other Partitions, and while the listed G1 ballistic coefficient of .490 isn’t considered very high these days, it’s not too bad. (I’ve confirmed that ballistic coefficient by longer-range testing in rifles chambered for various high-velocity 6.5mm rounds.)
What the 6.5-300 Weatherby Mag Is Good For
So what is the 6.5-300 Weatherby good for? Before becoming a factory cartridge, some long-range target shooters found it worked pretty well, especially for 1,000-yard benchrest shooting. Eventually, however, they grew weary of its recoil and short barrel life and started using smaller 6.5s designed around modern accuracy precepts, such as 30-degree shoulders, typified by the increasingly popular 6.5 Creedmoor.
As a result, the 6.5-300 Weatherby is basically a big-game round, and that’s reflected in Weatherby’s choice of bullets in its factory loads. Many older hunters consider 6.5s suitable only for “deer-sized” game, despite Scandinavian hunters successfully using the 6.5x55 to take uncountable numbers of moose over the past century. One counter-argument claims North American elk are harder to slay than European moose.
My experience on North American game larger than deer mostly involves elk, though there have also been plenty of caribou and some moose. Over the decades I’ve seen quite a few animals taken with cartridges many hunters think are too small for the job. In fact, a couple of my hunting partners have even taken elk with .25-caliber cartridges.
In 2014 my wife, Eileen Clarke, got picked in a computer lottery for an early-season cow hunt near our home. She chose to use the New Ultra Light Arms 257 Roberts that’s been her primary (but not only) big-game rifle during the past dozen years. The September weather was warm, so it took a few days to find the right elk, but eventually Eileen ended up 123 yards from a young but mature cow, quartering away across a small draw, and put a Barnes 100-grain Tipped Triple-Shock (TTSX) in the middle of the right ribs, aiming for the left shoulder. At the shot I expected the elk to go around 50 yards before falling, but instead it dropped right there, probably because the little TTSX clipped the bottom of the spine during its trip through both lungs. While skinning the cow, we found the expanded bullet under the hide of the left shoulder.
The other .25-caliber elk was a 6x6 bull, its antlers measuring around 300 inches, taken by my hunting partner Tim Frampton (who works for Weatherby), while hunting a ranch an hour from my house. Tim asked before the hunt if the 257 Weatherby Magnum was enough for elk, and some friends at Weatherby and I said yes. The bull was standing pretty much broadside on a steep mountainside, and at the shot, he galloped downhill until he ran head-on into a big Douglas fir, obviously dead on its feet. Oh, and the Nosler 120-grain Partition Tim used exited the bull’s chest.
On the other side of 6.5 caliber, I’ve seen plenty of big game, ranging in size from caribou and gemsbok to moose and bison, taken with the 270 Winchester, 270 WSM, and 270 Weatherby. The only “failure” was on a cow elk years ago, when a brand-new 150-grain premium bullet turned out not to be premium at all. Other than that, all the animals have died promptly, including a bull moose and a cow bison Eileen killed, both with typical lung shots using the 270 Winchester. The Shiras moose took a step and a half after a Nosler 150-grain Partition angled through its chest. The 900-pound buffalo went 40 yards before collapsing—and the Barnes 130-grain TSX exited, leaving an obvious blood trail.
Oddly, the animals I’ve taken and seen taken with various 6.5mm cartridges were all “deer-sized,” the rounds ranging from the 6.5x54 Mannlicher-Schoenauer to the 264 Win. Mag. But based on the plus-sized animals taken with 25s and 270s, I’d be willing to bet a new custom rifle that the 6.5-300 Weatherby will work fine on elk. It’s obviously more gun than the 270 Winchester, despite the 0.264-inch bullets being a fingernail’s thickness smaller in diameter.
The big advantage of the 6.5-300 Weatherby isn’t so much sheer power, though obviously it has plenty, while not recoiling any more than a typical 7mm magnum. Instead, its big advantage is the super-flat trajectory, combined with bullets that drift very little in the wind. A flat trajectory may be out of style among some hunters, who depend on twirling the elevation knob when making longer shots. I’ve done plenty of that myself, but sometimes big game doesn’t give us much time to laser ranges or carefully measure wind velocity or even think. An accurate, flat-shooting 6.5mm cartridge can make quick shots much easier when we need to shoot now.
6.5-300 Weatherby Mag Load Data