Reloading The Versatile .300 Winchester Short Magnum.
By John Barsness
Like many new cartridges, the .300 Winchester Short Magnum wasn’t a new idea when it appeared in 2001. Shorter, fatter cartridge cases had been stuffed into bolt actions for quite a while, but the trend really got going after WWII, when Remington introduced their 722 bolt action with a magazine about 2.85 inches long. Two wildcatters, Roy Gradle and Fred Wade, designed beltless “magnum” cartridges to fit in 722 magazines by lathe-converting .348 Winchester brass into rimless cases remarkably similar to the .300 WSM.
However, their wildcats never became popular, mostly because the .375 and .300 Holland & Holland had connected “magnum” with belted cases in shooters’ minds, and provided plenty of belted brass for conversion into cartridges including the .300 Weatherby and .300 Winchester Magnums.
As a result several decades passed before short, fat, beltless magnums gained a foothold, thanks to more rifle companies producing short bolt actions. Remington remained the major player, producing not only the Model 722 (which in 1962 became the short Remington 700 action) but the Remington 600, 660 and 7, which were so successful other companies had to follow. Winchester was among the last, finally introducing a short-action Model 70 in the 1980’s.
While Remington had introduced their 6.5 and .350 belted short-action magnums in the 1960’s, they didn’t really provide “magnum ballistics,” partly because their belted cases limited capacity due to the relatively small diameter ahead of the belt. In fact, with bullets seated deeply to fit in a short magazine, the .350 actually has slightly less powder room than the .35 Whelen, a fine cartridge but not a “magnum.”
Barsness has used the .300 WSM on animals from coyotes to elk.
This bull was taken in New Mexico with a Nosler Model 48 rifle.
By the 1990’s the abundance of short bolt actions and resurgence of African hunting resulted in another solution. The booming safari business revived many older African cartridges, including the .404 Jeffery, a beltless round with a rim diameter almost identical to belted cases. When cartridge companies reintroduced .404 brass, wildcatters had a “new” case functioning in bolt actions designed for belted magnums.
They claimed several advantages, including increased case capacity in cartridges of the same length, lighter-weight rifles due to short actions, and even higher velocities due to case shape burning powder more “efficiently.” The last wasn’t a new claim. In the section on Roy Gradle’s 7mm Express in P.O. Ackley’s Handbook for Shooters and Reloaders, published in 1962, Ackley notes: “Higher velocities are claimed with the relatively short fat case, as compared to the longer, and slimmer cases of equal capacity.”
So far no major pressure laboratory I’ve contacted has found this magic. Instead they report in cartridges of the same caliber, similar powder capacity results in similar pressures and velocities. The real reason extra velocity occurs in wildcats is more pressure.
Wildcat loads are typically “worked up” until cases show signs of distress, whereupon powder charges are reduced slightly. This normally results in more pressure than in commercial cartridges, because the maximum 65,000 PSI allowed for any cartridge by the Sporting Arms and Ammunition Manufacturer’s Institute (SAAMI) is far below the level where brass cases show “pressure signs,” such as the imprint of the ejector hole on the face of the case-head.
SAAMI sets 65,000 as absolute max because they recognize several factors can raise pressures above “normal,” especially temperature. The 65,000 psi limit provides a safety margin in warm weather, but working up loads to case-distress levels and backing off a little does not. (This is exactly why 7mm STW factory ammo has never obtained anywhere near its wildcat velocities.) Yet Winchester claimed some case-shape velocity magic for the .300 WSM when it appeared, apparently so they could also claim it matched .300 Winchester Magnum velocities despite the WSM’s smaller powder capacity.
The real reason the .300 WSM’s 2,970 feet per second with 180-grain bullets slightly exceeded the velocity of the .300 Winchester Magnum’s 180-grain factory load was the .300 Winchester was somewhat underloaded. Today SAAMI allows 180-grain .300 Winchester Magnum ammo to beat the .300 WSM by over 100 fps—also true of pressure-tested handloads back in 2001.
However, the magic-shape claim was a definite help in publicizing the new round. In 2002, a Winchester representative told me they’d sold eight times as many .300 WSM’s as marketing surveys had predicted. It was the most triumphant introduction for any new big game round since the 7mm Remington Magnum in 1962.
The case shape did have one positive effect on ballistics: The short powder column and relatively sharp 35-degree shoulder angle allowed powders to burn more consistently than in longer rounds. SAAMI maximum pressures aren’t based only on averages. One other standard is how widely pressures vary in a string of individual rounds. Velocities in the .300 WSM vary less than in longer .300 magnums, so ammo can be loaded safely to slightly higher pressures than the .300 Winchester Magnum without individual rounds going over-max.
More consistent velocities also result in finer accuracy. This may not be apparent in every factory rifle, but is a definite overall trend. The handloads tested here were chosen from published data mostly for potential velocity, though sometimes the data noted more accurate powder. Even so, any factory big game rifle that averages 0.99 inch for 4-shot groups with nine handloads that haven’t been tweaked for the most accurate powder charge, or bullet seating depth, is very accurate.
I’ve owned three .300 WSM’s over the years, and hunted with three others borrowed from various companies. One interesting mini-trend in new rifles is a slight lengthening of the magazines in short bolt actions, apparently started by high ballistic-coefficient bullets recently favored for longer-range hunting.
The maximum overall length of the .300 WSM listed by SAAMI is 2.86 inches, the same as in 2002, but the “Portuguese” Model 70 Winchester I purchased a couple of years ago has a 3.05-inch magazine. This is long enough to allow the ogives of such bullets as the Berger Hunting VLD’s and Nosler Long Range AccuBonds to easily be seated close to the rifling, yet still allow loaded rounds to fit in the magazine.
The .300 WSM recoils less than larger .300 magnums,
so the range sessions were reasonably comfortable.
The most accurate load used the 185-grain Berger Hunting VLD and
IM4350 powder, but all the loads averaged slightly under an inch.
Weight And Recoil
Does the .300 WSM work? Yes it does, though the claim of lighter rifle weight is exaggerated, since short and long bolt actions of the same brand only differ by 3 or 4 ounces. Walnut stocks can easily vary this much simply due to wood density, so any larger difference in weight is due to the slimmer barrels some companies put on .300 WSM’s.
But because the .300 WSM produces somewhat less velocity than other .300 magnums, it also produces somewhat less recoil—or in lighter rifles, about the same amount of recoil. My Model 70 weighs 7 pounds, 14 ounces, with a 6×36 Leupold, and while the range sessions for the listed handloads weren’t exactly restful, they were more pleasant than shooting larger .300 magnums.
I took my first big game animal with the .300 WSM the year before it was introduced, a pronghorn buck in Wyoming, and since then have used it on everything from coyotes to elk. It works very well as an all-around big-game cartridge, as well it should, since it falls neatly into the ballistic slot between the .30-06 and the larger .300 magnums. While it isn’t selling like it did 15 years ago, it’s by far the most commercially successful short, fat, beltless magnum and should remain popular among hunters for a long, long time.
John Barsness’s latest book, The Big Book of Big Game Hunting, is scheduled to appear in September 2017, and can be ordered from Rifles And Recipes, P.O. Box 579, Townsend, MT 59644-0579, (406) 521-0273, www.riflesandrecipes.com.