To make the .204 Ruger, the .222 Remington Magnum case was necked down to .204 inches (5 mm) and its shoulder moved forward and angle increased to 30 degrees.
[7] To achieve these velocities, the factory uses a proprietary powder composition known internally as SMP746, specially formulated by Primex, and, as of 2013, not available to handloaders.
The propellant features a de-coppering agent (bismuth pellets) that helps prevent fouling.
Reloading data from Hornady, using commercially available powders, indicate velocity peaking at just under 4,200 ft/s (1,300 m/s) with the 32-grain (2.1 g) bullet in longer barrels.
The .204 Ruger was intended primarily for varmint rifles, which require bullets with flat trajectories but not much mass or kinetic energy.
The resulting cartridge provides somewhat higher velocities than any of these, giving a maximum point blank range of more than 270 yards (250 m).