The Hornady Manufacturing Company introduced the .17 Hornady Mach 2 (.17 HM2) in 2004. The .17HM2 uses a .22 LR case that has been extended and necked down. This cartridge should not be mistaken for the Hornady .17 HMR which is based on the case of a .22 Magnum. The 17HM2 is designed to take varmint at 100 yards and more, and performs the task admirably. The .17 HM2 develops a similar amount of energy as the .22 LR in foot pounds, but it travels at a higher velocity. This higher velocity results in a flatter bullet trajectory. The point of impact rises less than one inch at 50 yards if it has been zeroed at 100 yards.
Today Savage, Browning and other manufacturers chamber rifles for the .17 HM2 . The most common actions are semi-automatic and bolt action, but there are also some quality examples of single shot rifles. The .17 HM2 has also been chambered for revolvers and semi-automatic pistols. Ruger 10/22 owners can even fire the .17HM2 from their rifles with a special conversion kit.
Hornady and CCI currently make .17HM2 ammunition available with bullets weighing 17 grains, while Hornady also sells a bullet weighing 15.5 grains. Both of these bullets exit the muzzle at more than 2,000 feet per second and carrying 150 foot pounds of energy. Shooters have reported successful shots on small vermin with the .17 HM2 out to 150 yards.
Varmint hunters today choose the .17 HM2 for the flat trajectory, accuracy that is less than one MOA, and light recoil, all factors combining to help it stand head and shoulders above other rimfire cartridges.