This is straight from Winchester's press release announcing the new cartridge:
The .17 Win Super Mag offers the downrange performance of a centerfire cartridge at only a fraction of the cost. For the first time in history, hunters can expect pinpoint accuracy and devastating performance from a rimfire cartridge at ranges well past 200 yards.
“Our engineers have been developing the top-secret .17 Win Super Mag caliber for more than three years and the rimfire revolution begins now,” said Brett Flaugher, Winchester Ammunition vice president of sales, marketing and strategy. “At 3,000 feet per second it’s the fastest modern rimfire cartridge on the planet. The downrange energy deposited by the .17 Win Super Mag will be a game-changer for varmint and predator hunters everywhere.”
The .17 Win Super Mag will initially be offered in three bullet types: a 20-grain plastic tip in the Varmint HV® (High Velocity) line, 25-grain plastic tip in the Varmint HE® (High Energy) line and a 20-grain jacketed hollow point in the legendary Super-X® line. Each .17 Win Super Mag bullet will far surpass the long-range wind drift and bullet-drop limitations of popular rimfire calibers like .22 Win Mag and .17 HMR, while depositing more than 150 percent more energy than both.
“Part of the appeal of rimfire ammunition to high-volume shooters is the relatively low cost,” added Flaugher. “With the launch of .17 Win Super Mag, now hunters will get the downrange performance of a centerfire cartridge at the more affordable price point of traditional rimfire ammunition. It’s the best of both worlds for our customers.”