.17 Winchester Super Magnum, is a rimfire rifle cartridge developed by the ammunition company Winchester in 2012. It descended from the .27 caliber nail gun blank by necking down the blank case to take a .17 caliber (4.5 mm) bullet. Initial loadings will be a 20 grain bullet, delivering muzzle velocities around 3000 ft/s .
Currently available is the Winchester Varmint High Velocity Ammunition 17 Winchester Super Magnum in either the 20 & 25 Grain Box of 50. The cartridge at 20 grain = 3000 fps and 25 grain = 2,600 fps. Currently, rifles firing the 17 WSM are the Savage B-Mag bolt action, Winchester 1885 Low Wall single shot, the Volquartsen semi-automatic, and the semi-automatic Franklin Armory F-17. The F-17 is the first gas-operated rimfire firearm, designed to handle the higher pressures of this cartridge.