17 HMR, is a rimfire rifle cartridge developed by the ammunition company Hornady in 2002. It was developed by necking down a . 22 Magnum case to take a . 17 caliber (4.5 mm) projectile. Commonly loaded with a 17 grain (1.1 g) projectile, it can deliver muzzle velocities in excess of 775 m/s (2,650 ft/s).