I was researching pictures of the Stechkin OTS-38 (revolver that fires silent 'captive-piston' ammo) and in the middle of those photos appeared a shot of the Jacob Shaw Jnr. revolver.
Under-Hammer Percussion Revolver by Jacob Shaw Jnr.
It is - like the modern current Stechkin - fired from the bottom chamber of the six shot .30" calibre cylinder.
The 1857 patented revolver has an interesting 'two-stage-action' that is a form of "Double-Action" in that it may be fired using the large main trigger to cock the hammer and rotate the cylinder then continue the long pull to finally fire the shot .. or the large trigger may be used to rotate & cock the hammer first while setting the second trigger - then that second trigger at the rear bottom inside the trigger guard is used as a hair trigger for precise accuracy at range.
It looks daft to talk about long-range shooting with this small 'pocket pistol' (3.25" tall x 5.5" long) - however it does have a sighting system that is not obvious in that first photo.
The cylinder pin has an extendable / retractable five inch hollow tube sight that is used by sighting at the small front pin on the barrel through the revolver from the rear and this is meant for use with the set trigger.
This very compact .30"calibre under-hammer revolver had an octagonal barrel variously recorded as both 4" and 3.25":
Information and photographs are hard to find - as although maybe as many as x50 guns were built there seems to be only one known example today.
Russian Stechkin OTS-38 Fires From Bottom Cylinder
- The Top 'Barrel' is a Laser.
Note: I've written a couple of posts before - some stuff about the Stechkin OTS-38 - earlier on 16th July 2014 and on 6th July 2014.. an interesting gun with useful features in my humble. - In service use since 2002 - with their internal troops since 2012 so very much current issue.