The .17 Hornet, also known as the .17 Ackley Hornet, is a .17 caliber centerfire rifle wildcat cartridge originally made by P.O. Ackley in the early 1950s.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 20grain "Superformace" V-max projectile at a published velocity of 3650fps.  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.
The .17 Remington was introduced in 1971 by Remington Arms Company for their model 700 rifles.
It is based on the .223 Remington, necked down to .172 in (4.37 mm), with the shoulder moved back. It was designed exclusively as a varmint round, though it is suitable for smaller predators. There are those such as P.O. Ackley who used it on much larger game, but such use is typically not recommended.
Extremely high initial velocity (over 4000 ft/s 1200 m/s), flat trajectory and very low recoil are the .17 Remington's primary attributes. It has a maximum effective range of about 500 yards (460 m) on prairie dog-sized animals, but the small bullets' poor ballistic coefficients and sectional densities mean they are highly susceptible to crosswinds at such distances.
The smaller .172 bullet typically has a much lower ballistic coefficient than other typical varmint calibers, such as that of the .223 Remington. Because of this, the .172 bullet loses velocity slightly sooner and is more sensitive to wind; but by no means does this render the cartridge useless. The advantages of this cartridge are low recoil, flat trajectory, and minimal entrance wounds. The tiny entrance wound and usual lack of exit wound on coyote-sized animals makes it an ideal round for fur bearing animals which the hunter intends to collect a pelt from. A significant disadvantage is the rapid rate at which such a small-caliber rifle barrel can accumulate gilding metal fouling, which is very detrimental to accuracy and may also eventually result in increasing pressures caused by the fouling's constriction of the bore. Many .17 Remington shooters have reported optimum accuracy when the bore is cleaned after every 10 - 20 shots, though more modern metallurgy used in both barrels and bullets has largely mitigated the alleged fouling issue.
The .17 Remington is also one of the few cartridges in which powder charge weight is often greater than bullet weight. Though this condition has been known to degrade accuracy, the .17 Remington is noted for exceptional accuracy. This reputation for accuracy is undoubtedly due in no small part to the fact that only good quality bolt action and single shot rifles have been so chambered from factory. Because the cartridge is based on the .223, it can also be used in the AR-15 and Ruger Mini-14 semi-automatic rifles by simply replacing the barrel.
And there are also the .17 caliber rimfires.
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