In 2004, the Hornady Manufacturing Company introduced the .17 Hornady Mach 2 (.17 HM2) using a .22 LR case that had 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 .17 HM2 is designed to take varmint at 100 yards or more, and performs the task admirably. It develops a similar amount of energy as the .22 LR in foot pounds, but it travels at a higher velocity – resulting in a flatter bullet trajectory.
Today, manufacturers still chamber rifles for the .17 HM2 – including Savage, Browning and others. 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, and Ruger 10/22 owners can even fire the .17 HM2 from their rifles with a special conversion kit.
Hornady and CCI currently make .17 HM2 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 carry 150 foot pounds of energy – which is why shooters have reported successful shots with the .17 HM2 on small vermin up to 150 yards.
Varmint hunters today choose the .17 HM2 for the flat trajectory, accuracy, and light recoil – all factors that combine to help it stand above other rimfire cartridges.