A redesign of an earlier trapdoor system, the Springfield 1873 was the first standard-issue breech-loading rifle adopted by the US Army. It saw lots of action in the battles with the American Indians, including at The Battle of Little-Bighorn. To the left is a picture from 1866 of Apache Chief Geronimo holding a Springfield Trapdoor rifle.
The rifle was named for its hinged breech block, which opened like a trapdoor allowing rapid loading of the single-shot weapon. With a barrel nearly 33 inches and an overall length of 52 inches, the rifle used .45-70-405 bullets: that means .45 caliber, 405-grain bullet propelled by 70 grains (4.5 grams) of black powder. With that kind of firepower, it was an effective weapon for the shooter.
Springfield also made the 1873 rifle in a half-stock, shorter barrelled carbine version, which fired bullets with less powder—and less recoil—for mounted cavalry soldiers.
The 1873 trapdoor was originally designed to fire copper cartridges rather than brass, but they expanded more in the breech, causing jamming. While a foot soldier could drop back and use a knife blade to clear the jam, a cavalry soldier found himself carrying a rifle that was only useful as a rather fancy club.
The black powder Model 1873 continued to be the main service rifle of the U.S. Military until it was gradually replaced by a bolt-action rifle using smokeless powder in 1892. It still was used by secondary units during the Spanish–American War in Cuba and in the Philippines,
By the way, if you include a Springfield 1873 Trapdoor in your story—or any black-powder weapon—remember the shooter can’t hide. The haze of bluish smoke would give away their position every time.