The .17 Hornady Magnum Rimfire, or .17 HMR, was developed in 2002 by the Hornady ammunition company. It is the one of the hardest hitting and most accurate rimfire rifle cartridges available today.
Although it is the child of the .22 Winchester Magnum Rimfire, the .17 HMR was one of many attempts to recreate the ballistics of the 5 mm Remington Magnum Rimfire. The RMR was produced during the 1970s and at the time was the fastest rimfire cartridge available. With RMR barrels and ammo near impossible to find it was discontinued in search of an easier to produce alternative.
The .22 WMR casing was chosen over the RMR because it requires a special bolt and magazine. The WMR casing was also more readily available as well as larger and stronger than other .22 LR. With this casing a simple barrel swap was all that was needed to produce weapons capable of firing the round.
Although the .17 HMR blows past the muzzle velocities and trajectories of the RMR and WMR, its downrange energy potential is still less than than the RMR. This still leaves an area open for further production of an even more powerful rimfire round in the future.
The first HMR rifles and ammo hit the market in 2002. Rounds are available in hollow point, soft tip, and FMJ from numerous companies.
While this round is a little much for small game like squirrel and rabbit up close, it is perfect for taking down larger animals such as raccoon, opossum, and fox. There have been videos of people using them to take coyote and hogs, but unless it's within 50 yards and a very well-placed shot it is not recommended by any manufacturer.