During the first week of January 2013, Winchester Ammunition sent me a press release about a most exciting new cartridge development, the .17 Win Super Mag, which has been under development in the utmost secrecy for over three years. This is a rimfire cartridge that launches a .17 caliber (.172" diameter), 20 grain bullet at the unheard of muzzle velocity (MV) of 3000 fps, making Winchester Ammunition's new cartridge the fastest rimfire cartridge ever developed. In fact, its velocity is solidly in the realm of high velocity centerfire cartridges. In a sense, Winchester's new .17 Super Mag completes the range of .17 caliber varmint cartridges that began (commercially) in 1971 with the .17 Remington.

The .17 Remington was the first standardized .17 cartridge and its velocity and general ballistic performance essentially duplicated the over 4000 fps MV of the .220 Swift, the long time velocity champion among American .22 caliber cartridges. However, although rifles and ammunition are still available, the .17 Remington never really caught on with the general shooting public. A few dedicated varmint shooters tried the .17 Remington and liked it, but most probably could not see much advantage in an "oddball" caliber that duplicated the .220 Swift, already established for decades prior to the introduction of the .17 Remington. The fact that the .17 Remington burned less powder and created less noise and recoil than the .220 escaped the notice of most shooters, who never tried the cartridge.

There matters stood, with the .17 being a specialty caliber barely recognized by most shooters, until the introduction of the .17 HMR in 2002. The rimfire .17 HMR is based on a necked-down .22 Magnum case loaded with a 17 grain bullet and it achieves a MV of 2550 fps. It offers near .22 Hornet centerfire ballistics to rimfire shooters at a considerably lower price and without the hassle of reloading. It is a brilliantly accurate and effective varmint cartridge with a maximum point blank range (+/- 1.5") of about 165 yards. For the first time, a rimfire cartridge was treading on the ballistic heels of a centerfire varmint cartridge. Shooters embraced the .17 HMR concept in great numbers and, finally, a .17 caliber cartridge became a best seller. This did not escape the notice of the major ammunition manufacturers.

In late 2007, Remington introduced their .17 Remington Fireball, based on a necked-down .221 Fireball case and in 2012, Hornady doubled down on their success with the .17 HMR by introducing the .17 Hornet, a centerfire .17 based on a blown out and necked-down .22 Hornet case. In factory loaded form, these two .17's offer ballistic performance at what is essentially .22-250 levels. The little .17 Hornet launches a 20 grain bullet at 3650 fps and the .17 Rem. Fireball launches a 25 grain bullet at 3850 fps. We now had .17 caliber varmint cartridges that could be compared to the .22 Hornet, .22-250 and .220 Swift; three of the four major velocity niches occupied by established centerfire .22 varmint cartridges. However, this left one glaring hole in the .17 caliber line-up, a medium range cartridge between the rimfire .17 HMR and the centerfire .17 Hornet, with MV in the .221/.222/.223 range of 2995-3240 fps.

With the advent of the .17 Win Super Mag, we have such a cartridge and, completely unexpectedly, Winchester has managed to do it in rimfire form. Rimfire cartridges are much less expensive to manufacture (and therefore to sell to consumers) than centerfire cartridges. While most centerfire rifle cartridges are sold in boxes of 20, rimfire cartridges typically come in boxes of 50. 50 rounds of rimfire ammo typically cost much less than 20 rounds of centerfire ammo. Rimfire ammo (which cannot be reloaded) eliminates the economic necessity for reloading, which many high volume shooters find a tedious and time consuming chore. The .17 Win Super Mag sounds like a win/win proposition on the performance and price fronts.

The technical details of just how Winchester Ammunition managed this breakthrough have yet to be released. In the past, the performance of rimfire ammunition has been limited by the inherent weakness of rimfire case design. The priming compound of rimfire cartridges is contained in the hollow case rim, which must therefore be thin and soft enough to be crimped by the blow of the rifle's firing pin to initiate powder combustion. Therefore, rimfire cases are necessarily thinner and weaker than centerfire cases, which have solid case rims. This has always limited the maximum pressure at which rimfire cartridges can operate. The .22 WMR and .17 HMR are based on the strongest cases that can be reliably fired by the rimfire method of ignition, at least up until now. The .17 Super Mag case is considerably larger than that of the .17 HMR and holds more powder. How Winchester has managed to keep the new cartridge's Maximum Average Pressure (MAP) within safe rimfire operating limits has yet to be explained. I can only speculate that yet another step forward in powder technology has made this miracle possible.

Winchester is initially introducing three loads for the .17 Super Mag. These include a Varmint HV (high velocity) load using a 20 grain Plastic Tip bullet at a MV of 3000 fps (#S17W20), a Super-X load with a 20 grain JHP bullet at the same MV (#X17W20) and a Varmint HE (high energy) load with a 25 grain Plastic Tip bullet at a MV of 2600 fps (#S17W25). These three loads are offered in 50 round boxes or 1000 round cases. Presumably, the Super-X load will be the least expensive, since the HV and HE loads are in the premium Winchester Supreme ammunition line.

These loads easily outperform all previous rimfire varmint cartridges, particularly the .17 HMR and .22 WMR, in both wind drift and trajectory. The .17 Win Super Mag claims accuracy and trajectory adequate to reliably hit rodents at ranges beyond 200 yards. It claims 150% of the .17 HMR's downrange energy to ensure humane, one shot kills. Complete specifications for the .17 Win Super Mag loads have yet to be released, but Guns and Shooting Online has requested ammunition for testing. Winchester says that guns and ammo will be available to consumers in local gun shops and sporting goods stores by April 2013.

Winchester's initial press release did not include trajectory information about the .17 Super Mag loads, but assuming that Winchester's 20 grain Plastic Tip bullet (SD .097) is similar in form to the Hornady 20 grain V-Max bullet (in the press release they look identical), which has a ballistic coefficient of .185, I should be able to come close. Here is the MPBR (+/- 1.5") trajectory for the 20 grain V-Max at 3000 fps MV, calculated for a 1.5" sight height using standard conditions (range / bullet path / velocity / energy):

Muzzle / -1.5" / 3000 fps / 400 ft. lbs.
25 yds / -0.3" / 2872 fps / 366 ft. lbs.
50 yds / +0.6" / 2747 fps / 335 ft. lbs.
75 yds / +1.2" / 2626 fps / 306 ft. lbs.
100 yds / +1.5" / 2508 fps / 279 ft. lbs.
125 yds / +1.5" / 2394 fps / 254 ft. lbs.
150 yds / +1.0" / 2283 fps / 231 ft. lbs.
175 yds / +0.2" / 2175 fps / 210 ft. lbs.
200 yds / -1.1" /2069 fps / 190 ft. lbs.
225 yds / -2.9" / 1966 fps / 172 ft. lbs.
250 yds / -5.3" / 1867 fps / 155 ft. lbs.

The MPBR of that load is 207 yards (+/- 1.5"). Put your scope's crosshair at the top of a standing, medium size varmint's head at 225 yards and the bullet should go through his chest at 225 yards. For comparison, the centerfire .222 Remington factory load with a 50 grain PSP bullet (BC .175) at a MV of 3140 fps has a MPBR of 212 yards. All of this is a long way of saying that, ballistically, the .17 Win. Super Mag is the rimfire equivalent of a medium range .22 centerfire varmint cartridge. Stay tuned, we will be reviewing a .17 Win Super Mag rifle as soon as we can get our hands on one and some ammo to shoot.