what model firearms ???

Need detailed description of all markings on weapon.

Breech loading firearms can be reloaded much more quickly, they can be reloaded when moving, and they are easy to reload when lying down. The muzzleloader must be loaded when standing upright.

Not just the US, but all military forces- for the first time, you could fire and reload quickly- while not standing up! Breech loading firearms meant a rifleman could fire from cover, and not while standing exposed to enemy fire.

About the time of the American Civil War- in the 1860s. The Spencer was a cartridge firing, breech loading, rifled repeater. The Burnside used a metal cartridge and a tape primer. The Sharps (as in Sharpshooter) used a paper cartridge, but was a breech loader. One breech loader saw limited use by a few British soldiers during the American revolution- the Howe. It was a flintlock, but loaded from the breech.