John Hancock Hall (1781-1841) partnered with Dr. William Thornton (1759-1828) (architect of the United States Capital building) to develop a new, ultimately-patented, breech-loading flintlock-based firearm. In the arrangement, both the breech lock and chamber were a single component so, when the breech was tipped upwards, it provided clear access to the chamber for reloading. As most firearms of the day featured muzzle-loading - a rather time consuming process in the heat of battle - the breech-loading method was a highly coveted one for infantrymen as reload times were decidedly decreased with the improved access.
Hall was born in Maine and became a firearms engineer after his time in military service. The patent was issued in 1811 and eventually resulted in the Model 1819 Hall Rifle (detailed elsewhere on this site) for U.S. Army service. Much of the work was completed at the famous Harpers Ferry Arsenal of Virginia (now West Virginia) where Hall himself spent no less than five years working to fulfill Army contracts. His Model 1819 was the first breech-loading firearm to be adopted as standard anywhere in the world.
As with most flintlock-based guns used during the Civil War, the Model 1819 Hall Rifle became a viable candidate for conversion to the percussion cap system. The flintlock approach had dominated battlefields for 200 years prior but it was susceptible to environmental factors and cumbersome to reload. The percussion cap system worked in much the same way as a child's cap pistol, a cap actuated by a falling hammer causing the ignition of propellant - the resulting force then propelling the bullet down the barrel and out of the muzzle.
The Model 1841 Hall Rifle was the result of work conducted by the United States Army to reproduce the Hall Rifle as a percussion-based weapon. Thousands were ultimately circulated in this form during the war with early models varying little from their flintlock counterparts. Only later was a revision made to the long gun in which a different breech release catch (something like a claw protrusion bending rearwards) being used and this set in front of the trigger guard. The ram rod was still held in a channel under the barrel and a long-running wooden stock was in play. The weapon was banded at two places along its length for rigidity and the available sights were of iron (front and rear).
The Model 1843 was the percussion cap-based shorter-length carbine form of the original Model 1819 Hall Carbine.