The .25-21 Stevens is an obsolete and discontinued American centerfire rifle cartridge.
Designed by Capt. W. L. Carpenter, 9th U.S. Infantry, in 1897, the .25-21 was based on the longer .25-25. It was Stevens' second straight-cased cartridge (after the .25-25) and would be used in the single shot Model 44 rifle, as well as the Model, which first went on sale in 1903. In addition, it was available in the Remington-Hepburn target rifle.
While the .25-25 was popular, the .25-21 offered "practically the same performance and was a little cleaner shooting." It was also found the usual black powder charge of the shorter, bottlenecked .25-21 offered "practically the same ballistics" as in the .25-25. It was highly accurate, reputedly capable of generating groups at .
In power, the .25-21 was outpaced by the .25-20 Winchester and .32-20 Winchester, while today, even modern pistol rounds such as the .38 Super offer superior performance.