In the 1860s, at the dawn of the self-contained metallic cartridge era, the military armsmakers of Great Britain and other major powers decided to alter existing muzzleloading rifle-muskets into breechloaders. Reasons included saving production costs and buying time to permit experimentation.
Rollin White’s 1855 patent for a bored-through cylinder was not just clever in its own right, it was also responsible for other inventors coming up with unique designs to try and circumvent it.
Double-action handguns have been available since at least the 1830s, though in the “pepperbox” form.
A reader inquires why is the ’03 Springfield is accorded so much fame.