Adolph Otto Niedner (October 1, 1863 – December 27, 1954) was an American gunsmith remembered for pioneering work with cartridges including the .22 Long Rifle and .25-06 Remington.

He enlisted in the United States Army in 1880 and fought against the Apache uprisings led by Victorio and Geronimo.

He served on the Milwaukee, Wisconsin police force until moving to Malden, Massachusetts in 1899 to work as a weaver in his father's business manufacturing linen socks.

Niedner worked with members of the Massachusetts Rifle Association, including gun barrel-maker Harry Pope, making tools and rifles for ballistics expert Franklin Ware Mann, and prototype Patridge gun sights for inventor Eugene Patridge.

Niedner manufactured custom rifles for many noted riflemen including Townsend Whelen, Charles Newton, and Ned Roberts.