Remington derringer dating
Each barrel then held one round, and a cam on the hammer alternated between top and bottom barrels.
The Remington derringer was in .41 Short caliber and achieved wide popularity.
The Philadelphia Deringer was a small percussion handgun designed by Henry Deringer (1786–1868) and produced from 1852 through 1868.
A popular concealed carry handgun of the era, this pocket pistol design was widely copied by competitors, sometimes down to the markings.
The back action lock was a later, improved design among locks, which had its spring and mechanism located behind the hammer, where it was thereby protected from dirt, fired cap residue, and gunpowder residue unlike earlier front action locks that had their springs and mechanism located directly in the path of such residue in front of the hammer, under the tube.
It could be seen in flight, but at very close range, such as at a casino or saloon card table, it could easily kill.
(The purpose of the patch on the ball was to keep the ball firmly lodged against the powder, to avoid creating what was called a "short start" when the ball was dislodged from being firmly against the powder.) A new percussion cap would then be placed on the tube (what today would be called a nipple), and the gun was then loaded and ready to fire.
(The half-cock notch prevented the hammer from falling if the trigger were bumped accidentally while carrying the handgun in one's coat pocket.) Then, to fire the handgun, a user would fully cock the hammer, aim, and squeeze the trigger.
A Remington-pattern derringer in .38 Special is still smaller than the most compact .25 ACP semiautomatic, and provides superior terminal ballistic performance to the .25 ACP.
While the classic Remington design is a single-action, manufacturers have also made double-action derringers, including some four-shot models, with the barrels stacked in a 2 × 2 block.