Fastest rimfire in the US


It certainly seems that the .17 is the calibre of the moment.

First the world was stunned with the performance of the .17 HMR, only to be less than bowled over by the .17 Mach 2.

Last year saw the launch of a new centrefire in the same calibre, with Hornady releasing the .17 Hornet, and more recently I began field testing this lightweight foxing contender.

Now another .17 is vying for attention, but what could possibly be on offer that isn’t already available? Let me introduce the .17 Winchester Super Magnum.

Officially launched at this year’s SHOT Show in Las Vegas, Winchester has brought another .17 rimfire to the market.

Apparently under secret development for three years, the new calibre becomes the fastest rimfire cartridge in the world, hurtling a 20-grain bullet at a staggering 3,000fps.

Compare that with the previously unrivalled .17 HMR and it’s more than 600fps faster. At these speeds, it sits beside high velocity centrefire cartridges.

This is quite a feat of engineering, as rimfire calibres have always been restricted by the inherent weaknesses of the design, forcing chamber pressures to be kept down.

This has previously held them back from competing at centrefire velocities. Winchester is yet to release the fine details of how it has managed this, but like the .17 HMR I am sure considerable jumps in powder development had something to do with it.

The origins of this calibre are unusual, as the case is based on a .27 calibre nail gun blank, which Winchester manufactures as part of its power fastener division.

Being longer and about 50 per cent thicker than the HMR case, it was able to handle much higher pressures. The new WSM generates around 33,000psi, compared with a relatively modest 26,000psi for the HMR. This translates to higher muzzle velocities and stronger down range performance.
But what are the actual field results of Winchester’s innovation? To start with, things are a little vague as Winchester is yet to put up full ballistic data on its website.

From what we do know, we can surmise that with a 100-yard zero, the new WSM will drop just over 4in at 200 yards, whereas the HMR shooting the same 20-grain bullet will drop 9.9in.

At 300 yards the WSM drop is 16in while the HMR plummets by more than 36in. In terms of down range energy delivery, the current HMR bowls over rabbits at 200 yards with 75ft/lbs and 1,305fps.

This seems a little less impressive when stood beside the WSM, which still runs at 2,070fps and punches 190ft/lbs. What is possibly more important, though, is wind drift, which is more than 7in less than the HMR at 200 yards with a 10mph wind.

The above numbers are impressive, but are worth nothing if the new calibre can’t shoot. Unfortunately I can’t comment on the accuracy of the round as we are yet to see it arrive on home shores.

However, I am sure Winchester has done its homework and testing, and that the .17 WSM will follow the HMR, and even the Mach 2, in being a very accurate shooter.

Bear in mind that the HMR saw its popularity hindered in the early days. Misfires and split case necks became an increasing annoyance, and my own experience of the Mach 2 showed that similar issues were still occurring up to the start of last year.

Hopefully the knowledge of these issues has been taken on board for this new development, and we won’t be plagued with the same frustrations going forward.

Sadly, we are unlikely to see any .17 WSM action before the start of next year, so we will have to hold tight until then, keeping an eye on the US forums for that latest updates. There will be three variations available, but the 20-grain ballistic tip will probably find most favour:

■ Varmint HV 20-grain Plastic Tip @MV 3,000fps
■ Varmint HE 25-grain Plastic Tip @MV 2,600fps
■ Super-X 20-grain JHP @MV 3,000fps

Given that Winchester has launched the new calibre in conjunction with Savage, the first offerings will undoubtedly be available in its own models. I hear news of a new rimfire from Savage to specifically support the .17 WSM. Let’s hope it’s a bit nicer than the M25 used to push the .17 Hornet.

Byron Pace

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Posted in Ammunition, Centrefire, Features, Reviews

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