“real” 7mm WSM, The

“real” 7mm WSM, The

Sundra, Jon R

When Winchester introduced the .300 WSM, the author couldn’t wait for it to develop the 7 mm WSM, so he necked it down himself. When Winchester released the factory 7 mm WSM, it didn’t match Sundra’s efforts. Here’s why.

I’m not one to get overly excited about a new cartlidge, but I have to admit that when the Winchester folks unveiled the .300 Winchester Short Magnum in September 2000, they had my attention. I had already done a lot of shooting and load development work with similar cartridges, Lazzeroni’s 7.21 Tomohawk (.284-cal.) and 7.82 Patriot (.308-cal.) Short Action Magnums, and knew how efficient these squat cartridges were.

By “efficient,” I mean a cartridge that extracts more velocity per grain of powder than one of identical capacity but having longer, more slender powder column like, say, the .270 Win. or .280 Rem. The shorter, fatter powder column puts more of the powder charge closer and off to the sides of the primer flame. The result is more efficient combustion that allows optimum velocities to be reached with lesser amounts of slightly faster-burning powders. Another bonus is that, all other things equal, the less unburned powder and gases being pushed down the bore, the less recoil.

With a major ammo manufacturer such as Winchester bringing out the .300 WSM, it put this newest technology within the reach of Joe Average-I’m talking the widespread availability of guns, ammunition and unprimed brass at affordable prices. Along similar lines, it was Remington that brought super magnum performance to the masses with its Ultra Mags.

Anyway, as much as I liked the .300 WSM as it was, knowing its case capacity was approximately 80 grs. of water-which is about five less than a 7 nun Rem. Mag.-I thought it would make an even better .28 caliber. So when I had the opportunity a few weeks after Winchester’s announcement to field test a pre-production Winchester Model 70 in.300 WSM, I brought home a plentiful supply of once-fired brass and sent a couple of them off to Steve Hornady to have dies made. “Just give me a die that necks these puppies down to .284,” I told him, “with no other changes.”

Not that it would have made a difference either way, mind you, but I was sure the folks at Winchester would be doing the same thing sooner or later. I mean, there was no way they weren’t going to establish a whole family of cartridges on this short magnum case; I just wanted to beat them to the punch where the 7 mm was concerned.

While I was awaiting my dies, the folks at E.R. Shaw ordered a reamer based on the empties I had sent them, and installed one of their premium barrels on a short Ruger 77 Mk II action I had sent them. Viola-six weeks before the .300 WSM was formally introduced to the world at the 2000 SHOT Show, and a couple of months before guns and ammo started reaching dealers’ shelves, I had my 7 mm WSM … or at least I thought that’s what I had! But you know what they say about the best-laid plans

Sure enough, the following September, exactly one year after rolling out the .300, Winchester announced not only a 7 mm version, but a .270 as well. According to the Winchester press release, both were derived by simply necking down the .300 WSM case–just as I had done, with no other changes. By that time, I had acquired two more “7 mm WSMs,” one built for me by Mark Bansner of Bansner’s Ultimate Rifles, based on the Model 70 short action with a Lilja barrel; the other was another Ruger Mk II barreled by Shaw, but this one on a standard length action so I could seat the bullets out as far as I wanted.

But then a funny thing happened. About a month after the initial press release announcing the .270 and 7 nun WSMs (which, by the way, was accompanied by spec drawings showing that both were simply necked-down versions of the .300), a second release was issued saying that the previous specs applied only to the .270, and that the 7 mm version would be delayed because of revisions.

To make a long story short, it was discovered that in some preproduction Winchester Model 70s and Browning A-Bolts it was possible to chamber a 7 mm WSM cartridge in a .270 WSM rifle. Not good. To preclude that possibility, Winchester’s design team decided to increase the body length of the 7 mm by 0.038″, thus increasing headspace and shortening the neck commensurately (overall case length remained the same). In one fell swoop, my three “7 mm WSM” rifles were relegated to wildcat status and technically were now “7/300 WSMs.” That’s what I meant about the best-laid plans!

As an interesting sidebar, had the Winchester folks done a little homework, they would have discovered that Remington went through the same thing back in 1956 when it was about to unveil the .280 Rem. Initially, the cartridge was to be like the .270 Win., i. e., derived by simply necking down the .30-’06, but stopping at .284″ instead of .277″. But Remington, too, discovered that under some circumstances involving minimum-spec ammo and a maximum-spec chamber, it was possible to cram what was technically a 7 mm-’06 into a .270 Win. rifle. That’s why when the .280 Rem. was introduced in 1957, its body length (headspace) was 0.051″ longer than that of the .270. So much for pertinent background information.

The change in specs delayed the debut of the 7 mm WSM by some four months. We received our test rifle-a pre-production Browning A-Bolt Stainless Stalker, along with preproduction ammo, in early April. Now an increase of 0.038″ in the body length of a cartridge is not a lot; in fact, it’s the thickness of 19 of the pages you’re now reading, yet you can see the difference when the 7 mm is stood next to its siblings, especially the .270.You can see that the 7 nun version stands taller in the body and is shorter in the neck. Naturally, this results in an increase in volume, slight though it is. As near as I could measure, the “genuine” 7 mm WSM holds about 1.5 grs. of water more than my wildcat version. For comparison’s sake, that makes it virtually identical with Lazzeroni’s 7 mm Tomahawk, and 9 grs. more than Remington’s 7 mm Short Action Ultra Mag.

Because the shooting and preparation of this article was done before the official announcement of the revised cartridge, I was curious as to whether or not there were any changes anticipated in the nominal ballistic specs that had been published previously. So I called Glen Weeks, the engineer in charge of the WSM project. According to Glen, they were actually able to average between 25 to 30 f.p.s. more with the slightly longer case, but the company had no plans to revise the specs upward. I think that’s a mistake. In the advertising/marketing game, any advantage you can claim over the competition is a plus, even if it’s only 25 to 30 f.p.s. I say, if ya’ got it, flaunt it!

For testing, all three of the loads that will be offered this year were sent: the 140-gr. Ballistic Silvertip and 160-gr. Fail Safe in the Supreme line and the 150-gr. Power Point in the Super-X line. The nominal specs as taken from Winchester’s 2002 catalog show the 140-gr. BST load as exiting at 3225 f.p.s.; the 150-gr. Power Point at 3200 f.p.s. and the 160-gr. Fail Safe at 2990 f.p.s. Respective mu=le energies are 3,233,3,410, and 3,176 ft. lbs.

To ready the A-Bolt for the range, I mounted a Nikon 4-1210 44 nun scope using Gentry’s excellent rings and bases. Ready to go, the rig weighed 8 lbs., 8 oz. I find it strange that Browning opted to go with 23″ barrels in all WSM chamberings, while U. S. Repeating Arms went with 24″ in all Winchester Model TOs. Then there’s Remington, which chose 22″ for the Model Seven, the only gun presently chambered for its SAUM’s. Personally, I like a 24″ barrel for everything but a dangerous game rifle, in which case I like a 22″ pipe, and a whitetail rifle, for which I prefer a 20″ spout.

The first thing I wanted to do was chronograph 10 rounds of each of the three factory loads to see how they matched up to the velocities claimed. Of the three, the 160-gr. Fail Safe produced the highest relative velocities by averaging 3020 f.p.s.; that’s 30 f.p.s. faster than spec. Remember, too, that the test gun wore a 23″ barrel, while nominal specs are established in 24″ barrels, so that would account for a loss of around 25-30 f.p.s. all other things being equal. That means the batch of ammo I had was actually producing about 50 f.p.s. over spec, or around 3040 f.p.s.! And there were no signs of stiff pressures, either, like excessively flattened or cratered primers, or brass flowing into the ejector hole and being burnished by the bolt face. Bolt lift was also normal.

The other two loads proved to be not quite on the same hormone regimen as the Fail Safe. The 140-gr. Ballistic Silvertip, for example, averaged 3,185 f.p.s. for a 10-shot string, and the 150-gr. Power Points clocked a mean of 3130 f.p.s. Add 25 f.p.s. to compensate for the 1″ shorter spout and we’re looking at realistic muzzle velocities of around 32 10 f.p.s. for the former, and around 3160 for the latter. When compared to the claimed 24″ test barrel figures, neither is far enough astray to worry about, as 25 f.p.s. plus or minus is normal from one barrel to the next, all other things being equal.

As for accuracy, I expected the 140-gr. BST to turn in the best accuracy, but it was the 150-gr. Power Points that produced the tightest groups. Here’s how they stacked up from benchrest at 100 yds.:

That’s decent enough accuracy, considering the test gun had a fullfloating barrel, which is unusual. Generally speaking, only the thicker, stiffer barrels found on varmint/target rifles are set up floating. Most production-grade sporter-weight rifles are set up to apply dampening pressure at the fore-end tip because thinner-contour barrels generally shoot better that way. As a rule, a sporter-weight barrel that’s floated will not shoot quite as well as one that’s dampened, but it will tend to shoot to the same point of impact from season, tn to season. Depending on the amount of pressure being applied and the stability of the stock, a dampened barrel could shoot “iddy biddy” groups, but the rifle could be temperamental as to where it places them on the target. Also, it can make a gun finicky as to how and where the fore-end is gripped and where it’s rested on a sandbag or other rest. Me, I’ll take consistency of zero on a hunting rifle over grouping, provided of course there’s not a drastic difference between the two.

So what’s the verdict now that the real 7 mm WSM has finally put in its appearance? Well, obviously, it doesn’t do anything ballistically that a 7 mm Rem. Mag. can’t do. Oh, if you want to split hairs, sure, the WSM will squeeze a few more f.p.s. on average, but in the field that’s meaningless. However, it does what it does with a better– designed, more efficient case that requires less powder and delivers slightly less recoil. Also, because it headspaces on the shoulder rather than a belt, it has the potential for better average accuracy and longer case life. Add all those little advantages up and, I for one, would be hard pressed to come up with any cogent reason for buying a belted magnum.

BY JON R. SUNDRA, Contributing Editor

Copyright National Rifle Association of America Sep 2002

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