Interesting gun, pretty awkward to hold, not a speed shooter. The ring under the trigger is pulled back to cock the hammer. Releasing the ring after the hammer is cocked moves the cylinder forward and up against the barrel, forming a gas seal. The first pic shows it with a (Pietta) Colt 1860 .44 (same year as the Savage & North)
Note the gap between the cylinder and barrel when the ring is back in the 3rd pic, but it's gone in the 4th pic.
Note the gap between the cylinder and barrel when the ring is back in the 3rd pic, but it's gone in the 4th pic.