The .204 Ruger is a centerfire rifle cartridge developed by Hornady and Ruger. At the time of its introduction in 2004, the .204 Ruger was the highest velocity commercially produced ammunition, and the only cartridge produced commercially for bullets of .204 inch/5 mm caliber.The 204 Ruger was developed from the .222 Remington Magnum, which has the second largest case capacity in the family that began with the .222 Remington. Only the European 5.6x50 Magnum is larger, which itself is a lengthened version of the 222 Remington Magnum. The 222 Remington Magnum provides about 5% more usable (below the neck) case capacity than the most popular member of the family, the NATO 5.56×45 mm (.223 Remington). To make the 204 Ruger, the 222 Remington Magnum case was necked down to .204 inches (5 mm) and shoulder moved forward and angle increased to 30 degrees. Bullets available in .204 caliber range from 26 to 55 grains (1.7 to 3.25g).