The oldest cartridge design still in large-scale production today, the rimfire suffers the ill effects of creation in the pre-center-fire period. Weaknesses stem from the ignition source; brass in the rim area must be thin enough to ensure detonation of the priming compound contained within when struck by the firing pin. Reduced-thickness brass necessitates low-pressure loadings, which result in lackluster external and terminal ballistics. As such, early, large-caliber rimfire cartridges have faded into obscurity, only chamberings best suited to plinking and small-game hunting remain. Development of new rimfire cartridges in the past half-century, and the past two decades in particular, have mostly been .17-cal.—commonly termed “sub-caliber”—cartridges. Although offering downrange advantages over stalwarts, such as the .22 Long Rifle, relatively mild pressures have prevented new cartridges from escaping the rimfire ballistic realm—until now. Enter the .17 Winchester Super Magnum (.17 WSM).

Rewriting The Rules
“Winchester is constantly striving to push the envelope on delivering faster, more powerful products in all categories to give our customers the advantage in the field,” said Brad Criner, senior product manager for Winchester Ammunition. The .17 WSM delivers upon this statement, and then some; however, achieving such performance proved problematic.

“The initial concept was derived more than a dozen years ago, and in direct development on this cartridge for a little over three years” reported Criner. “It took that long for technology to be developed to build the robust case that could withstand the higher pressures needed to drive a .17-cal., 20-grain bullet 3,000 fps.”

What advancements were made to enable the creation of the 33,000-p.s.i. .17 WSM cartridge? “Until now, the higher pressures split necks and burst rims, preventing us from introducing a cartridge of this magnitude,” he said. “In recent years, we developed a proprietary process for building the necked-down .17 HMR cases to significantly improve case strength and functionality. The same technology allowed us to develop the .17 WSM.” For comparison sake, the SAAMI-set maximum average pressure (MAP) for the .17 HMR is 26,000 p.s.i.

Fortunately for Winchester, it already had a basis—albeit unconventional—to which it could apply insight garnered from the aforementioned project—.27-cal. Powder-Actuated Tool (P.A.T.) loads for the construction industry that the company had loaded since the 1960s. “Why reinvent the wheel?” said Criner. The case, modified to handle the increased pressure rating, held sufficient propellant to achieve the desired velocity.

Choosing the ideal bullet caliber/weight proved simple for Winchester. “The .17 cal. has a great ballistic coefficient (BC), fit within the envelope and offered the highest velocity,” explained Criner. “We achieved our 3,000-fps goal and then some. We are safely hitting that number and could possibly get a little more but 3,000 fps allowed us to check the box on exceeding the ballistic performance of any rimfire magnum and approach center-fire ballistics (we actually exceed the ballistics of the .22 Hornet).” Thus far, Winchester has three bullet options: 20-grain red polymer tip (V-Max), 20-grain hollow-point and 25-grain polymer tip (gray), the latter of which has a factory-touted velocity of 2,600 fps.

Why not .20 caliber? Even if Hornady’s ultra-lightweight, 24-grain 0.204-inch-diameter NTX was used, the desired velocity for the cartridge could not be met; velocities would be similar to the 25-grain, .17-cal. polymer-tip load. The less-streamlined, light-for-caliber, .20-cal. bullets also exhibit notably lower BCs than .17-cal. projectiles of similar weight; the result is less energy downrange, as well as additional drop and wind deflection.

“That being said, we have not ruled out other ballistic possibilities in the future,” said Criner. “We are exploring options of different bullet calibers and other shell case calibers (P.A.T. is also loaded in 22- and 25-cal. shell cases).”

Performance in relation to cost determines a rimfire cartridge’s success and, ultimately, longevity; cite the .17 HMR (introduced in 2002) as an example of a widely accepted newer option, while the .17 Mach 2 (unveiled in 2004) is fading into obscurity—shooters are unwilling to pay a premium for the cartridge’s moderate ballistic advantages over the aged, yet immensely popular, .22 Long Rifle. Concerning downrange performance, as will be soon illustrated, the .17 WSM is on-par with center-fire cartridges; however, perusing MidwayUSA’s website, the three options range in price between $14 and $16.30 per 50. How is that possible?

“There are two primary drivers to the cost advantage of rimfire product versus a center-fire product,” reported Criner. “First, the primer is physically part of the rimfire case and does not need to be separate as is required for center-fire products. Secondly, the production process steps used in a rimfire are considerably less than those of a center-fire product, which includes multiple machining steps to create the intricate head and rim.”

What about availability? “We have ensured that the .17 WSM will be loaded on a regular basis in our magnum rotation,” he said.

Breaking Down The Ballistics
How does the .17 WSM “stack up” to its rimfire relatives and center-fire cousins? Despite its relatively petite size, with a maximum cartridge overall length of 1.590 inches and body diameter of 0.269 inches, the cartridge compares more favorably to the latter; however, any examination wouldn’t be complete without first contrasting it to the cartridge that enabled its existence, the .17 HMR.

Although not a true “apples-to-apples” comparison, due to the fact that the 20-grain V-Max loaded in the .17 HMR has a lower BC—.125—than that used in the .17 WSM (.185), with identical bullet weights, just assertions can be formulated. According to factory-published data, the .17 HMR propels the 20-grain V-Max to 2,550 fps, and with a 150-yard zero, the projectile impacts 1.7-inches high at 100 yards, 5-inches low at 200 yards, and 14.7-inches low at 250 yards. With a modest, 10-m.p.h. full-value wind, the bullet deflects off course 3.3 inches, 15.4 inches and 25.7 inches, respectively, at those same distances. Propelled to 3,000 fps from the .17 WSM, the more streamlined (and tougher, due to differing construction) 20-grain V-Max strikes 0.8-inches high at 100 yards, 2.5-inches low at 200 yards and 7-inches low at 250 yards. Deflection measurements are 1.6 inches, 8 inches and 13.6 inches less than those of the .17 HMR at the same distances. Considering the size of the game pursued, this is noteworthy.  Interestingly, despite its lower muzzle velocity, thanks to its higher BC (.230) the 25-grain polymer tip experiences slightly less wind deflection beyond 200 yards.

Equally important, the bullet from the .17 HMR reaches its lower threshold for expansion (about 1,400 fps) just beyond 175 yards, while that from the .17 WSM—upsetting down to 1,600 fps—works beyond 300 yards. With this, the .17 HMR’s heaviest bullet option is 20 grains, whereas the .17 WSM is available with a 25-grain projectile. Energy figures illustrate a consistent, 100 ft.-lb.-plus advantage out to 200 yards, and more than double the energy at 250 yards.

In actuality, the “more fair” comparison is between the .17 WSM and the relatively new .17 Hornet, a wildcat based upon the .22 Hornet legitimized by Hornady. Propelled to 3,650 fps from the .17 Hornet, the same 0.172-inch bullet as used in the .17 WSM hits 0.4-inches high at 100 yards, 1.5-inches low at 200 yards and 4.3-inches low at 250 yards. Wind deflection at those distances are 1.3 inches, 5.6 inches and 9.2 inches, respectively, or 0.4 inches, 1.8 inches and 2.9 inches less than the .17 WSM—a small advantage. Its bullet would expand at distances beyond 425 yards; however, 31.2-inches of wind deflection at said distance makes the argument irrelevant. Due to the significant “step-up” in velocity, downrange energy figures greatly favor the Hornet. The center-fire .17 Hornet does offer the benefit of reloadability, but .17 Hornet ammunition sells for between $18.50 and $20 per 25, so the end-user pays more and gets half the ammunition when compared to the .17 WSM—no small consideration for the high-volume shooter.