The Model 1873 was the fifth iteration in the Allin trapdoor design, named for the hinged breechblock which opened like a trapdoor. It was produced in two versions: an infantry rifle with a 32⅝-inch (829 mm) barrel, and a cavalry carbine with a barrel.
The cartridge was designated as ".45-70-405", indicating a .45 caliber, bullet was propelled by of black powder. It had a muzzle velocity of in the rifle, a powerful and effective load for the military skirmish tactics of the era. A reduced-power load of of powder (.45-55-405) was manufactured for the carbine, to lighten recoil in cavalry usage. It had a correspondingly reduced muzzle velocity of , and reduced effective range.
The rifle was originally issued with a copper cartridge and taken off to fight the American Indians in the American West during the second half of the 1800s, but the soldiers soon discovered that the copper expanded in the breech when heated upon firing and sometimes jammed the rifle, by preventing extraction of the fired cartridge case. A jam required manual extraction with a knife blade, and could render the rifle useless in combat except as a club.
After the annihilation of General George Armstrong Custer's battalion (armed with the carbine and .45-55 ammunition) at the Battle of Little Big Horn in 1876, jamming of their rifles was asserted to have been a factor. The rifle cartridges were redesigned with brass instead of copper cases, which did not expand as much. This proved to be a major improvement.
The men of the Army, after Little Big Horn, were required to take target practice twice a week on target ranges and became so proficient that many of them won awards that were offered by the armed forces for their riflemanship.