The 204 Ruger was the second Ruger-named cartridge produced by a partnership between Ruger and Hornady, the first being the big bore .480 Ruger revolver cartridge introduced in 2003 for the Super Redhawk. With the backing of a major gunmaker and a major ammunition company, the round was an instant success, with other ammunition makers and firearms makers quickly adding the new chambering. Ruger’s initial offerings included the bolt action Model 77 MKII, and the single shot Ruger No. 1, and Hornady offered loadings with 30-and-40-grain (1.9 and 2.6 g) bullets.
The .204 Ruger has proven to be a very accurate and efficient cartridge: an early tester reported 1/2 MOA groups at 100 yards (91 m) with the Hornady loads and a Ruger #1 Varmint rifle. This is not surprising, considering that the first cartridge in the family, the .222 Remington, was a top benchrest shooting cartridge for many years after its introduction.
The .204 Ruger was intended primarily for varmint rifles, which require bullets with flat trajectories but not much mass or kinetic energy. The .204 was “splitting the difference” between the popular .224 varmint rounds such as the .220 Swift and .22-250 Remington, and the tiny .172 caliber rounds such as the .17 Remington and the .17 HMR. The resulting cartridge provides somewhat higher velocities than any of these, giving a maximum point blank range of more than 270 yards (250 m).