Henry VIII (1491-1547) - way back in time had a breech-loading gun for shooting birds - but not until the 1800s were various needle-fire, paper cartridges, metallic rim-fire cartridges developed - and then centre-fire cartridges in 1857.
The New Zealand Government when faced with limited support from the "home" British government - in 1861 ordered Calisher & Terry breech-loading carbines - that fired a water-proofed paper cartridge - and in due course received between 3,000 to 4,000 guns. - Some of this model gun were used by Confederate soldiers in America.
Note: The Calisher & Terry company closed-down in 1870 as their design could not be adapted readily to use the new metallic cartridge.
Soldiers on both sides of the American Civil War, 1861 to 1865 - largely fought with muzzle loading weapons.
QUOTE: from Guns of The Old West by C E Chapel.
"After the battle of Gettysburg, fought on the first three days of July 1863, 37,574 arms were picked up from the battlefield and sent to Washington, D.C., for examination by ordnance experts. Of this number, 24,000 were found fully loaded. One fourth of these loaded guns had only one load in the barrel, but one half had two loads, and the remaining 6,000 arms had from three to ten loads in each gun.
Some of the muskets were loaded with the paper cartridges upside down so that the powder was not exposed to the ignition. One musket was found with twenty-three loads in the barrel, some right side up and some upside down. From all this evidence of the near-hysteria and excitement prevailing during the battle, the government authorities estimated that one third of the soldiers on each side were ineffective as fighting men. With a breech-loading arm, this multiple loading would be impossible;
I read years ago that if it is possible for anyone to fit something the wrong way round - there will always be somebody who will do it - and that's without the stress and panic of deadly warfare.
When these thousands of men were released from the conflict at the end of the civil war - many headed on West carrying their muzzle-loaders as an essential tool for the settlement of the Frontier lands.
Few could afford to buy the latest metallic cartridge, breech-loading weapons, or repeaters, - that were proven as so much more effective arms. Indeed some men even clung to the flintlock as a more independent system - it not needing a supply of percussion caps.