A close friend recently bought an 1866 model Springfield rifle in mint condition. As he and I researched the history of this weapon we uncovered quite a story:
At the end of the Civil War the U.S. government had thousands of Springfield rifled muskets, cal .58 in their armories. They petitioned the Springfield to work on converting them into cartridge rifles. The first attempt in 1865, the Allin conversion worked, but had flaws. The cartridge they came up with was made of copper, like the Henry and Winchester cartridges in use at the time. It was also rimfire, which did not adequately ignite the 70 grains of "musket" powder it contained. The copper also tended to expand in the chamber and resist extracting. Springfield left the ramrod under the barrel for this purpose.
The process they used was to cut out part of the breech and install a "trapdoor" receiver on top to allow insertion of the cartridge. In addition, they bored out the barrel and inserted a steel sleeve, which they rifled, necking the caliber of the bullet down from .58 to .50 caliber. The designation of this cartridge was the 50/70/460, the first number denoting the caliber, the second the grains of powder used, and the last the weight of the bullet. That was quite a slug. With this new rifle an infantryman could fire ten times the number of shots per minute as he could have using the muzzle-loader.
By 1866 Springfield adopted the first center-fire cartridge developed by Steven Benet of the Frankford arsenal. This new cartridge ignited the powder fully, though the copper cartridges still sometimes expanded and had to be punched out. By 1868 this powerful cartridge was in its final form and also adopted for use by Sharps and Remington.
The model 1866 saw heavy usage in the plains wars (notably the Wagon-Box battle in Wyoming) and in the Apache wars in Arizona and New Mexico Territories. It was replaced in 1872 by a new model Springfield, 45/70, which remained the U.S. Army's rifle of choice for the next 33 years, when it was replaced by the bolt action Krag-Jorgensen, caliber 30-40.
These of 50/70s are as tall as a man and weigh over 10 pounds. My friend tells me they can be found for about $950 -- a cheap price for that kind of history.
The original conversion of the Springfield rifled musket to a breechloader occurred in 1864. CPT Erskine S. Allyn & MAJ Hiram Berdan designed a drop-in breechblock which was welded in place in a .58 cal musket's bbl & took a .58 cal rimfire ctg. In 1866, using the many, many M1863 rifled muskets the US had left over from the War Between the States, muskets were bored out to .63 cal, a .50 cal steel insert was put in the bbls, & an Allyn/Berdan breechblock installed. The ctg was a .50-70-450 load--.50 cal, 70 gr 'common rifle powder (abt Fg modern terms) & a 450 gr semi-flatnosed slug. In 1868 a new rifle, with a purpose-made bbl & breechblock but using stocks & other furniture from M1863 muskets, still in the .50-70-450 cal, was issued. The M1866 conversion breechloaders were what were used at the Wagon Box fight. It wasn't until the 1870s that the rifle in the new .45-70-500 cal was issued, using a .458 cal semi-flatnose lead slug weighing 500 gr. The later Springfield carbine used a .45-55-405 load because the shorter, lighter carbine kicked like a govt mule with the heavier infantry load. For years the only commercial load available for the '.45-70' was actually a low-pressure, smokeless-powder version of the carbine load. If you wanted more power, you had to load it yourself.
The original load for the 45-70 was a 405 bullet, the 500 didn't come out till 1881 when if was figured out the 500 improved range. The original ones also used the Benet centerfire system where they were not reloadable and a hollow rimmed copper case. This had a tendency for the extractor to rip the rim when the rifle was hot.
Whether this was part of the problem at the Little Big Horn will be debated for ever.
From last year, here is a friend shooting an 1868 Trapdoor in a Grand Army of the Frontier match near Sargent Nebraska:
Part of Curly Crow's testimony at the inquiry following the disaster included "....man sit down, work on gun.