Springfield (Model 1866, Second Allen Conversion)

This rifle was a single-shot breechloader, which chambered a .50/70 metallic cartridge. The Model 1866 was created by taking a muzzle-loading .58 caliber Springfield rifle and brazing in place a .50 caliber sleeve in the bore. A hinged trapdoor was installed at the base of the barrel that accepted the metallic cartridge.