HALL'S M 1819 Rifle & M 1843 Carbine:

Hall's Breech-Loading design marks a significant advance from the then standard MUSKETS .. but  they don't seem to be at all well known .. they haven't been much lodged into 'The Halls Of Fame' for firearms eh 😃.. There are multiple iterations and combinations of the 'Hall's' .. which is partly because these weapons were built right from the start with interchangeability of parts.

The flintlock M1819 Hall's Rifle was the first breech loading long arm adopted by the military in USA - and furthermore - the later Carbine version M1843 was also the first percussion ignited long arm adopted and issued by America.

As expected .. the Hall's were both praised and damned by the Officers of the day. The breech-loading design alone vastly increased the rifleman's rate of fire .. while the later combination with percussion cap ignition once again advanced the ease of fire while bringing greater reliability under stressful battlefield life .. BUT the breech loading design was imperfect in it's ability to seal and contain the gasses under pressure when firing - getting dangerously more leaky with wear over time.

One interesting feature of all Hall percussion firearms was that the entire breech-block could be removed and carried around as a very crude pistol - lethal at close range. - Many U.S. soldiers during the Mexican-American War commonly carried their loaded breech-block in their pockets when off duty - giving themselves added close quarter protection.

Hall's firearms were variously built in a range of bore sizes .. and issued as both smooth-bores and rifled versions - and as percussion-ignition & original flintlocks - many of which were subsequently converted to percussion fire.

Wikipedia as usual has a decent page on these: https://en.wikipedia.org/wiki/M1819_Hall_rifle

- and here is a brief "Forgotten Weapons" show-&-tell video:

https://www.forgottenweapons.com/hall-breechloading-carbine-at-ria/

.. There was a BAD SMELL later around the 'HALL CARBINE AFFAIR' when during the American Civil War, John Pierpoint Morgan financed the purchase of 5,000 surplus rifles at $3.50 each, which were then sold back to the government for $22 each. - Quite a scandal ensued and this may have resulted in these arm's importance being deliberately historically neglected. - Shhhh ..

https://en.wikipedia.org/wiki/Hall_Carbine_Affair

Marty K.