The .25-06 Remington had been a wildcat cartridge for about 35 years before being standardized by Remington in 1969. It is based on the .30-06 Springfield cartridge necked-down (case opening made narrower) to .257 inch caliber with no other changes. Nominal bullet diameter is 0.257 in (6.53 mm) and bullet weights range from 75 to 122 grains (4.9 to 7.9 g).