RIFLES
Short Magnum Trifecta
The wait is over--Winchester .270 and 7mm Short Magnums are here!
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Little more than a year has passed since Winchester Ammunition announced its revolutionary .300 Winchester Short Magnum, based on an original stubby, unbelted case that allowed .300 Winchester Magnum performance in a short .308-length bolt action. The .300 WSM was and is a great cartridge, but it was immediately obvious that the case had great potential for use with other calibers. . .and just as obvious that, in due time, Winchester would do exactly that.
A TOUGH CHOICE
Even during the initial introduction of the .300 WSM, gunwriters were already asking what would come next, and the Winchester folks were asking for our opinions. I lobbied heavily for a .270. Colleagues lobbied just as vigorously for a 7mm. As we all know, the actual bullet diameters are pretty darned close. Our only two .270 cartridges, the .270 Winchester and .270 Weatherby Magnum, use a .277-inch bullet, while the legion of 7mm cartridges the world over use a .284-inch bullet. A difference of seven thousandths of an inch (.007) is hardly worth arguing over--but shooters argue about it almost endlessly. Legions of American riflemen love their .270s, as do equally large legions of 7mm fans.
Knowing this, and personally favoring the .270, I was worried--I'm sure those who prefer the 7mm were equally worried. After all, these two similar and popular calibers were obvious candidates for the next WSM, and it seemed apparent that Winchester would have to make a choice. The solution was to make both, and to bring them to market simultaneously.
On the surface it might seem silly and somewhat confusing to launch two such similar cartridges simultaneously. After all, they share some of the same bullet weights propelled at similar velocities. And you have to look at them closely to tell them apart. If I were doing it I would have made a choice, but I'm no marketing specialist. Those who are considered correctly that there are .270 fans and 7mm fans. It's unlikely that many among us will want both a .270 and a 7mm WSM. But we now have two excellent new cartridges to choose from.
WINCHESTER'S SHORT MAGNUM
A short review may be in order. It's no secret some measure of efficiency is gained by using a powder column that is wider rather than taller. The powder in a short, fat case ignites and burns more efficiently than the same volume of powder in a long, slender case because the primer gas (flame) immediately accesses a greater percentage of the charge.
The difference isn't dramatic; you still need to burn more powder to significantly increase velocity. However, the primary restriction on cases most existing bolt actions will accept is length, not width--especially if you remove the unnecessary belt. So by using a fatter, unbelted case you can increase powder capacity.
Remington's Ultra Mag family is an example, incorporating a fat, unbelted .375 H&H-length case to obtain greater powder capacity than is possible with cartridges based on the .375 H&H.
Just last year Winchester developed its own unbelted case--but made it short enough to fit into short bolt actions. The initial result, the .300 WSM, uses a 2.1-inch case with a slightly rebated rim of .535 inches, and a base diameter of .550 inches. With a 35-degree shoulder and a relatively short neck, the case has only slightly less capacity than belted magnums based on the .375 H&H case cut down to fit into .30-06-length actions (nominally, a case length of 2.5 inches). In practice, the greater burning efficiency of the short, fat case makes up for the slight difference in powder capacity; the .300 WSM equals the .300 Win. Mag. in performance while burning about seven percent less propellant.
This difference alone isn't enough to get excited about. However, there are several side benefits. First, the WSM case can fit into a short bolt action, potentially reducing gun weight and bulk. Second, burning less powder reduces recoil. This is a mathematical fact, since the weight of the powder charge is one of the factors used to derive recoil velocity, which is then used to compute recoil energy. The problem with this is that, mathematically, the difference isn't all that great, while the difference in felt recoil between a .300 WSM and a .300 Win. Mag. of similar weight and feel is noticeable, so there must be some other dynamic involved with efficient ignition and burning that I don't fully understand.
Third, the burning efficiency of the short case is generally conducive to accuracy. This is why the .308 is generally regarded as more inherently accurate than the .30-06. Also, short actions are more rigid than long actions; rigidity promotes accuracy. Finally, the unbelted case design means headspacing will be on the shoulder, which is more precise than headspacing on the belt of a belted cartridge. This also promotes accuracy. The difference will not be seen in all rifles but, on average, a short, unbelted magnum should be more accurate than a rifle chambered to a longer, belted case of similar performance. Also, if everything is equal--quality of barrel, rigidity of action, precision of chambering and barrel/action mating, and consistency of ammo--most rifles chambered to short, unbelted magnums should be more accurate than rifles chambered to the longer-cased belted magnums.
The concept is thus sound, and initial sales suggest that the shooting public were good. So it was inevitable that Winchester would expand the line. Both the .270 WSM and 7mm WSM are nothing more (and nothing less) than the .300 WSM case necked down to the proper caliber. Case length is the same, as is the 35-degree shoulder angle. Performance, though, is different.
THE .270 WSM
Among American big-game hunters there are three popular bullet diameters that overshadow all others: .277, .284 and .308. Cartridges necked to both .284 and .308 are legion, but historically there have been just two commercial .270 cartridges: the .270 Winchester, introduced in 1925; and the .270 Weatherby Magnum. The latter cartridge was Roy Weatherby's first magnum, developed in about 1943. The .270 Winchester is based on the .30-06 case necked down to accept a .277-inch bullet. Long championed by the late Jack O'Connor, it quickly became a bestseller and remains a perennial favorite. The .270 Wby. Mag., based on a shortened and necked-down .375 H&H (or .300 H&H) case, is an incredibly fast, flat-shooting and effective cartridge that offers surprisingly low recoil in relation to its performance. Although an important part of the Weatherby lineup, I have never understood why the .270 Wby. Mag. isn't more popular; you'll find very few cartridges (none without significantly greater recoil) that shoot flatter than the .270 Wby. Mag.
Generations of American hunters grew up reading about Jack O'Connor's exploits with his .270 Winchester. Several of those generations are still with us. Americans still love their .270s. Bullet selection is extremely well-developed, and the .270 is rightfully considered one of the best choices for deer, antelope, sheep, goats and such. Even though I've never understood why the .270 Wby. Mag. isn't more popular, I have long thought there was room for a faster, modernized .270-caliber commercial cartridge. This perfectly describes the .270 WSM.
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