If you've been following this blog, you know that Winchester is unleashing the world's fastest rimfire cartridge. Until now, the details have been top-secret.

It's called the .17 Winchester Super Magnum, and it sets a new standard in rimfire performance by pushing a 20-grain bullet to 3,000 fps and a 25-grain to 2,600 fps.

Those are the quickest times ever posted by a commercial rimfire cartridge.

25-grain (left, gray tips) and 20-grain (right, red tips) Winchester Super Magnums.

That 3,000 fps from the 20-grain bullet is fast enough to more than double the downrange energy of both the .17-gr. V-Max in the .17 HMR and a 40-gr. bullet in the .22 WMR. But that's not all. The 20-grain Winchester shoots twice as flat as the .17 HMR and three times flatter than the .22 WMR. Wind deflection of this little Winchester bullet is two times less than that of the 17-grain Hornady.

Left to right: .22 Long Rifle, .22 WMR, .17 HMR,
two .17 Winchester Super Magnums    

An easier way to sum up the .17 Winchester Super Magnum is to compare it to the famous Winchester .22 Hornet. In a nutshell, the new .17 Winchester Super Magnum outperforms the old Hornet (introduced in 1933) in everything but retained energy, and at 250 yards even those number are awfully close. Shoot the 25-grain bullet in the new .17 and you surpass .22 Hornet energy at 250 yards. The real news—the stand up and cheer, “Oh boy, I've gotta get one of these!” news—is that the .17 Winchester Super Magnum does this for two-thirds less cost. That's right. The average, store-bought .22 Hornet cartridge will set you back about $1.00. The average .17 Winchester Super Magnum should ring up at around 30 cents.
    
I don't know about you, but those numbers ring my cash register.
    
So, where did this new rimfire come from? As you might know, most “new” cartridges evolve from older ones. The BB cap became the longer CB cap which was stretched to make the .22 Short, then the .22 Long and .22 Long Rifle. That case was stretched again to create the .22 Win. Mag., and that longer case was in turn necked down to make the .17 HMR. There was no stretching or necking of existing rifle cartridges in the making of the .17 Winchester Super Magnum. Its case was a .27-caliber powder reservoir used in industrial construction to drive fasteners into concrete. In converting it to a rifle round, Winchester engineers made it thicker and stronger to withstand the pressures inherent in pushing a bullet down a barrel. Then they necked it down to .17.
    
Full reports on the rifles being built to handle the round aren't yet available, but I imagine they'll need to be stronger than existing rimfire models. The .17 Winchester Super Magnum hits peak pressures of 33,000 psi. The .17 HMR peaks at 26,000 psi. I'm also assuming firing pin impact energy must be higher to crush the rim of the thicker cases for ignition. That this can be done was proven to my satisfaction last August when I got to shoot a couple of rough, pre-pre-production Savage bolt-action test rifles in Montana. Although I had to often hand feed one cartridge at a time and extract them with a knife blade, the rifles regularly printed five shots around MOA at 100 yards. Shooting was done outdoors in variable breezes gusting to 10 mph from a portable bench. One six-shot group at 200 yards clustered inside 2.25 inches. Not many jackrabbits, prairie dogs or foxes are going to escape that.

Two .17 Winchester Super Magnums with a Savage test rifle.    

By the way, I chronographed those rounds and recorded muzzle velocities slightly higher than Winchester is advertising. The 20-grain rounds averaged 3,023 fps and the 25-grain ones went 2,625 as measured 10 feet from the muzzle.

I also opened a round of each and found 9.5 grains and 8.5 grains of a fine ball powder in each, respectively. This tiny dose of powder is part of the reason the ammo will be so inexpensive. Not having to build and install primers into each case is another, and the minimum quantity of metal in both the brass and bullets seals the deal.
    
When the .17 HMR hit the streets about 8 years ago, there were skeptics and doubters. But that little speedster quickly proved its place. By essentially doubling .17 HMR performance, the .17 Winchester Super Magnum should be a huge hit. It will be deadly on the usual rodents up to and including chucks. It'll be perfect for jackrabbits and crows, and an ideal fur-getter on fox, bobcat and probably coyote. I can't wait to try it.