The .25-21 Stevens was an 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 44 1/2, 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 20 or black powder charge of the shorter, bottlenecked .25-21 offered "practically the same ballistics" as 24 or in the .25-25. It was highly accurate, reputedly capable of generating .5 in groups at 100 yd. 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.

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