The .17 Hornet, also known as the .17 Ackley Hornet, is a .17 caliber centerfireriflewildcat cartridge originally made by P.O. Ackley in the early 1950s. The cartridge was created by simply necking-down the .22 Hornet to .17 caliber. The result was a small case with relatively little noise capable of high velocity.
Ackley mentions it as one of the most balanced of the .17 cartridges of his time. 
This cartridge is now available as a factory loading; the 17 Hornet from Hornady uses a 20 grain (1.3 gram) "Superformace" V-max projectile at a published velocity of 3650fps (1113 metre/second).  However, the new standardized ammunition/brass is not built to the same dimensional specifications as the original wildcat or the dimensions listed on this page. Hornady's standard has a shorter body, shorter overall case length, and a thicker rim. Shooters wishing to use the Hornady product in a Wildcat .17 Hornet chamber will experience the bullet jumping to the rifling and lose the inherent accuracy the cartridge has been known for, if the rim thickness allows the firearm to function at all. Many firearms that have offered the Wildcat .17 Hornet depend on rim thickness for headspace. In such firearms, shooters may not be able to use the new ammo/brass without having their chambers modified for the thicker rims. This may allow the Hornady products to function, but again are likely to reduce accuracy significantly.