Winchester Varmint High Energy ammunition was developed as a hard-hitting, high performing line of rimfire ammunition for varmint and predator hunters. Varmint HE ammunition delivers excellent terminal performance producing quick, humane kills. The revolutionary 17 Winchester Super Magnum is the fastest, most innovative rimfire cartridge ever developed. Based off of a 27 caliber power fastener blank, this cartridge produces centerfire velocities and energy in a more cost-efficient rimfire package.Specifications: Muzzle Velocity: 2600 fps Muzzle Energy: 375 ft. lbs. Caliber: 17 Winchester Super Magnum Bullet Weight: 25 Grains